Immune checkpoint inhibitors in children with replication-repair-deficient high-grade gliomas. The South London Paediatric & TYA Neuro-Oncology Network experience

Immune checkpoint inhibitors in children with replication-repair-deficient high-grade gliomas. 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The South London Paediatric & TYA Neuro-Oncology Network experience Marta Perez-Somarriba, Anna Campello, Philip Benjamin, Zita Reisz, and 22 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9131402/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose High-grade gliomas (HGG) are the most common intracranial tumors in children with replication repair deficiency (RRD) syndromes. Defective DNA repair leads to a high mutational burden, providing biological rationale for immune checkpoint inhibitors (ICI). However, responses to ICI are heterogeneous, and resistance mechanisms remain poorly understood. We report on the experience of the Paediatric & TYA Neuro-Oncology South London Network (SLN) and collaborators on the safety and efficacy of ICI in RRD-HGG. Methods Clinical, histopathological, molecular, and survival data were collected from children with molecularly confirmed RRD-HGG treated with ICI at SLN between 2019–2023. Descriptive statistics were used for demographics. Survival outcomes were analyzed using Kaplan-Meier estimates and univariable Cox proportional hazards models. Results Six patients were identified (Lynch syndrome n = 4,constitutional mismatch repair deficiency n = 2). Median age 9.6 years (range 2.74–11.02). ICI was administered upfront, at relapse, or at both stages (n = 2 each). No grade 4–5 toxicities were observed. Two patients treated upfront achieved sustained responses of 14 and 26.5 months, with one remaining in complete remission at last follow-up. Median progression-free survival from first ICI exposure was 4.1 months (95% CI 0.13–8.06; range 0.6–26.5), and median overall survival was 11.1 months (95% CI 10.06–12.14; range 10.2–35.3). Conclusions ICI use in RRD-HGG is biologically justified, but optimal agents, combinations, and predictive biomarkers need yet to be fully determined. Given the rarity of RRD-HGG, international collaborations, such as the International Replication Repair Deficiency Consortium (IRRDC), are essential to advance treatment strategies for these patients. Replication-repair high-grade gliomas Immune checkpoint inhibitors survival biomarkers Figures Figure 1 Figure 2 Introduction Genetic variants in DNA mismatch repair (MMR) genes ( MLH1, MSH2, MSH6, PMS2 ) and/or DNA polymerases proofreading (PPD) genes ( POLE, POLD1 ) cause DNA replication repair deficiencies (RRD), predisposing children to an increased lifetime risk of cancer, including brain tumours. 1 , 2 Bi-allelic germline mutations in MMR genes define Constitutional Mismatch Repair Deficiency (CMMRD) syndrome. Virtually all individuals with this condition will develop cancer in the first two decades of life, with a new malignancy at an average of every 2 years. 3 Brain tumours are the most frequent cancer encountered, followed by haematological and gastrointestinal tumours. 2 , 3 Conversely, monoallelic germline MMR mutations define Lynch syndrome (LS) which predisposes to gastrointestinal and endometrial cancers in early adulthood. 4 Brain tumours have been sporadically described in adolescents and young adults with LS, but risk factors and prevalence remain poorly understood. In both conditions, high-grade gliomas (HGG) are the most common brain tumour. 5 , 6 Replication repair-deficient high-grade gliomas (RRD-HGG) account for 6% of all paediatric-type diffuse HGG (pHGG) and are considered a distinct subgroup genomically. 7 , 8 Histologically, are most often glioblastoma (WHO grade 4) or HGG not otherwise specified (NOS), with loss of MMR protein expression. They also display a distinctive hypomethylation pattern and cluster within a partially characterized group of HGGs previously designated “wild-type C” or “paediatric RTK1”. 5,8,9 These tumours exhibit high tumour mutational burden (TMB) (≥ 10 Mut/Mb), and/or microsatellite instability (MSI) 2 , 10 with even higher TMB when PPD genes are also altered. 11 , 12 RRD-HGGs have been generally treated according to institutional/national HGG guidelines 13 – 19 , achieving a median progression-free survival (PFS) of 9 months, and survival post-recurrence on conventional therapies less than 3 months. 20 Importantly, the immunogenic nature of RRD-HGG makes these tumours more prone to respond to immunotherapies, such as immune checkpoint inhibitors (ICI). 2 , 16 , 21 Clinical activity of ICI in paediatric RRD-HGG has been demonstrated by the International Replication Repair Deficiency Consortium (IRRDC), although optimal treatment regimens and timing remain undefined. 1 , 22 , 23 Given the rarity of RRD-HGG, conducting large-scale clinical trials to evaluate the best ICI of choice and/or optimal drug combinations can make it very challenging to persuade funders, industry partners, and regulators. We aim to expand the body of knowledge on the treatment of RRD-HGG with ICI based on our institutional experience to help guide future studies and therapeutic strategies. Methods Patients aged 1 to 25 years, diagnosed with RRD-HGG and receiving treatment with ICI within the South London Paediatric & Teenager and Young Adult Neuro-Oncology Network (SLN), which includes the Royal Marsden Hospital, St George’s Hospital and King’s College Hospital, together with The Institute of Cancer Research as academic partner, between 2019 and 2023 were eligible. Histological diagnosis was based on the 2016 or 2021 WHO classification of tumours of the central nervous system, depending on the year of diagnosis. RRD-HGG were defined based on loss expression of MMR proteins, germline MMR gene alterations, MSI and/or TMB ≥ 10 Mut/Mb. Clinical, radiological, histopathological, molecular and survival data were collected following approval from our institutional review board. Molecular, genomic, and immune profile analysis from patients included in the IRRDC registry was added, where available. PFS was defined from the first course of ICI (regardless of whether this was started at first line or relapse) to disease progression (according to RANO or iRANO criteria, where appropriate), death or last follow-up, whichever occurred earlier. Overall survival (OS) was defined from diagnosis to death or last follow-up, whichever occurred earlier. Adverse events (AE) were graded according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5. Survival outcomes were calculated using the Kaplan-Meier and univariable Cox proportional hazards methods. Statistical analyses were carried out using IBM SPSS Statistics v.30.0.0. Results Six patients were identified (3 males, 3 females). Demographic, clinical, radiological, histological, molecular, therapeutic, and survival data are summarised in Table 1 and germline and molecular findings in Supplementary Table 1 . Median age was 9.6 years (range 2.74–11.02). Five were supratentorial (83%), and one spinal. Germline testing confirmed heterozygous MMR gene variants (LS) in 4 cases (67%) and homozygous variants (CMMRD) in 2 (33%). Genomic and immune profile analysis from the IRRDC was available for 3 patients #2, #4 and #6 ( Supplementary Fig. 1; Supplementary Fig. 2) . ICI were used upfront after surgery in one case with a synchronous lymphoma (#5), and upfront after surgery and radiotherapy in three cases (#2, #4, #6). ICI were used at relapse in two cases who were ICI-naive (#1, #3) and in two who had already received ICI upfront (#2, #4); Fig. 1 . Table 1 Summary of demographics, clinical, radiological, histological and molecular characteristics, treatment, and outcome of six children diagnosed with RRD-HGG Median age (range) N = 6 % 9.6 years (2.74–11.02) Gender (F/M) 3/3 50%/50% Clinical features/symptoms at presentation Café-au-lait spots 4 67% Seizures 3 50% Headaches 2 33% Vomiting 2 33% Hemiparesis 2 33% Back pain 1 17% Familial history of MMR-deficiency 4 67% Underlying cancer predisposing conditions Homozygous deficiency (CMMRD syndrome) 2 33% Heterozygous deficiency (Lynch syndrome) 4 66% Germline gene alteration MLH1 1 17% MSH2 1 17% MSH6* 2 33% PMS2* 2 33% Location Supratentorial 5 83% Spinal 1 17% Histology Glioblastoma WHO grade 4 3 50% Anaplastic astrocytoma WHO grade 3 1 17% Pediatric High grade glioma WHO grade 4 2 33% Molecular tumor profile DNA replication repair protein deficits MLH1 2 33% MSH2 4 66% MHS6 4 66% PMS2 4 66% POLE/POLD1 2 33% Other molecular alterations IDH mutation 2 33% ATRX mutation 3 50% TP53 mutation 6 100% NRAS/MAPK mutation 2 33% Other tumors Synchronous tumor 1 17% Metachronous tumor 1 17% Treatment upfront Surgery** 6 100% Radiotherapy 4 67% Chemotherapy (concomitant and/or adjuvant) 2 33% Adjuvant ICI 4 67% Treatment at relapse (n = 5) Surgery*** 3 60% Radiotherapy**** 3 60% ICI 4 80% Median PFS from first ICI (95%CI / range) 4.1 months (0.13–8.06 / 0.6–26.5) Median OS (95%CI / range) 11.1 months (10.06–12.14 / 10.2–35.3) 95%CI: 95% confidence interval, CMMRD: congenital mismatch repair deficiency, F: female, HGG: high grade glioma, ICI: immune checkpoint inhibitor, M: male, MMR: mismatch repair deficiency, N/A: not available, OS: overall survival, PFS: progression-free survival, RRD: replication repair deficiency, WHO: World Health Organization. *MSH6 and PMS2 mutations: one heterozygous and one homozygous, each. **Partial resection (n = 4), subtotal resection (n = 1), gross total resection (n = 1). ***Biopsy, partial resection, and gross total resection (n = 1 each). ****Re-irradiation (n = 2), first-time radiotherapy at relapse (n = 1). The median PFS and OS (95%CI; range) were 4.1 (0.13–8.06; 0.6–26.5) and 11.1 months (10.06–12.140; 10.2–35.3), respectively. ICI were generally well tolerated. Grade 3 toxicities included hyperglycaemia, due to new onset of insulin-dependent diabetes and elevated ALT/AST. There were no grade 4 AEs. Toxicities are summarised in Table 2 . Case descriptions: Case #1 A 2-year-old female was diagnosed with a left fronto-temporo-parietal glioblastoma IDH-wildtype (WHO grade 4) with PMS2 loss. TMB, MSI, and the immune profile were unknown. Genetic studies identified a heterozygous germline variant in the PMS2 gene. She underwent partial resection of the tumour followed by chemotherapy according to HIT-SKK 92 protocol. After 3.7 months, the tumour progressed, and the child was enrolled on the pembrolizumab phase I/II trial (NCT02332668) in our centre. 24 No grade3/4 AEs were reported. After 3.7 months of treatment, a routine MRI showed progressive disease. The child died 10 months after the initial diagnosis. Case #2 An 8-year-old male presented with a left occipital lesion. Gross total resection (GTR) was achieved. Histology confirmed HGG/glioblastoma IDH-wildtype (WHO grade 4) with MSH6 and PMS2 loss. Germline studies confirmed homozygous variants in the PMS2 gene. Sequencing confirmed ultra-hypermutation (TMB: 432.8 mut/Mb) with mutations in POLE (p.A463D, p.S459F) , MLH1 and MSH6 , TP53, and NF1 . He received focal radiotherapy (54Gy) with concomitant lomustine, followed by pembrolizumab. The child also received a bespoke peptide vaccine plus GM-CSF privately for 12 months, as per parental decision, whilst on adjuvant pembrolizumab. Nineteen months after diagnosis, a new asymptomatic right frontal lesion was found on a routine MRI scan. The lesion was completely resected and consistent with HGG (WHO grade 4). Sequencing confirmed TMB of 457.1 Mut/Mb with MMR and PPD alterations, but a non-overlapping (< 0.3%) mutational profile, suggesting that this was a second primary tumour rather than a relapse (Supplementary Fig. 1.A) . The patient received focal radiotherapy (54Gy) followed by 4 additional cycles of pembrolizumab (total 26 cycles) whilst access to nivolumab/ipilimumab was being secured. After 2 cycles of nivolumab/ipilimumab, a routine MRI showed a thrombus within a pre-existing developmental venous anomaly in the fourth ventricle. ICI were put on hold, and the child was managed conservatively. In the meantime, the immune transcriptome analysis suggested a relatively low tumour inflammation score (TIS: 7.11 percentile 13.6) (Supplementary Fig. 2A, 2B) , possibly explaining the immune-escape on pembrolizumab. 23 , 25 Meanwhile, the child presented with signs of superior vena cava syndrome. A chest CT scan showed a large mediastinal mass. The biopsy confirmed lymphoblastic lymphoma (lymphocytic lineage could not be confirmed). The plan to resume immunotherapy was abandoned, and he started chemotherapy as per UKALL 2019 guidelines. The lymphoma responded, and the child entered in remission. He continued regular head MRI scans with no evidence of recurrence until 8 months after the lymphoma diagnosis, when a routine head MRI identified two dural-based lesions located in the right temporal pole and the left cerebellopontine angle. The biopsy of the right temporal lesion confirmed a pediatric-type diffuse high-grade glioma favouring RTK1 subtype on methylation (calibration score 0.99). Sequencing and analysis of mutational profiles were not possible at that time. Soon after that, the child presented an acute intratumoural bleed within the metastatic deposit in the left cerebellopontine angle. He subsequently deteriorated, requiring intubation and ventilation. After a multidisciplinary discussion limitation of further therapeutic effort were agreed with the family. The child died 36 months after the initial diagnosis ( Fig. 2 ) . *The child received 26 doses in total: 22 as part of his adjuvant treatment upfront plus 4 additional doses given until completion of focal radiotherapy after first relapse. **Nivolumab/ipilimumab interrupted after 2 cycles due to thrombus in a developmental venous anomaly in the fourth ventricle associated with mild triventricular dilatation (image not shown), followed by permanent discontinuation of nivolumab/ipilimumab due to intercurrent diagnosis of lymphoblastic lymphoma. Case #3 An 11-year-old female was diagnosed with a left frontal glioblastoma (WHO grade 4) with MSH6 loss and IDH1 R132H mutation (not classifiable on methylation). Germline studies confirmed a heterozygous variant in the MSH6 gene. The child underwent a partial resection followed by focal radiotherapy (54Gy) with concomitant temozolomide and adjuvant temozolomide/lomustine. After 2 cycles, the tumour progressed. The tumour was resected and the child was transferred to our institution to receive nivolumab and lirilumab within the AcSÉ-eSMART trial (NCT02613962). However, she failed screening due to further local tumour progression before treatment initiation. Surgery was performed with histology in keeping with recurrent glioblastoma (molecular investigations not repeated). She was then enrolled in the pembrolizumab trial (NCT02332668). 24 After one cycle, she developed neurological symptoms. An MRI scan confirmed tumour progression, and treatment was discontinued. TMB, MSI, and immune profile were unknown. She died 11.7 months after initial diagnosis. Case #4 A 12-year-old female with a family history of LS was diagnosed with a right parietal glioblastoma (WHO grade 4) with MLH1 and PMS2 loss (not classifiable on methylation) partially resected. Germline studies confirmed a heterozygous mutation in the MLH1 gene. She received focal radiotherapy (54Gy) with concomitant lomustine, followed by pembrolizumab. Sequencing demonstrated a TMB of 58 Mut/Mb, with pathogenic TP53 and NF1 variants. Analysis of the immune transcriptome suggested a moderately inflamed microenvironment (TIS: 7.96; percentile 52.4); Supplementary Fig. 2C . Her disease remained stable until seven months after diagnosis, when a routine MRI scan showed a new suprasellar mass associated with new central hypoadrenalism and hypogonadotropic hypogonadism. Tumour biopsy was consistent with paediatric high-grade glioma IDH-wildtype RTK1 type (calibration score 1.0) harbouring the same pathogenic TP53 variant and a TMB of 56.6 Mut/Mb. However, when compared with the first tumour, < 10% of variants were shared between both specimens (Supplementary Fig. 1.B) . She received focal radiotherapy (40Gy) followed by nivolumab. Unfortunately, after 3 cycles of nivolumab she presented clinical and radiological progression and treatment was discontinued. The patient died 11 months after initial diagnosis. Case #5 A 10-year-old male whose brother had died due to a T-cell lymphoma was diagnosed at another European centre with an abdominal mass. A head/spine MRI scan done as part of the routine diagnostic work-up identified a synchronous frontal lesion. The patient was neurologically asymptomatic. The abdominal mass was completely resected, and a subtotal resection of the intracranial lesion was achieved. The histology confirmed an abdominal Burkitt´s lymphoma and an anaplastic astrocytoma (WHO grade 3) with IDH1 mutation (R132H) and loss of expression of MSH2 and MSH6 . Germline testing confirmed a homozygous variant in the MSH6 gene. Methylation, TMB, MSI, and the immune profile were not available. Following surgery, the patient received rituximab (6 cycles) for the Burkitt´s lymphoma, achieving complete remission, alongside nivolumab for the HGG. No radiotherapy or chemotherapy was administered upfront. The anaplastic astrocytoma remained stable. Six months after diagnosis, an MRI scan showed tumour progression in the left hemisphere. By then, the family had relocated to the UK, and his care was transferred to our centre. He received focal radiotherapy (54Gy), but he continued to deteriorate and died 11 months after initial diagnosis. Case #6 A 4-year-old male with a family history of LS presented with back pain and loss of sensitivity in both legs. An MRI scan identified an intraspinal lesion between T8 and T12. The lesion was partially resected. The histology was consistent with HGG (WHO grade 4) with loss of expression of MLH1, MSH2, MSH6 , and PMS2 . Germline studies confirmed a heterozygous variant in the MSH2 gene. Sequencing and WES confirmed ultra-hypermutation (TMB: 307.69 Mut/Mb) with somatic mutations in POLE (c.641BG > A p.Glu2140Lys) , MSH2, MLH1, PMS2, TP53 , and NF1. Methylation profiling classified the tumour as paediatric-type diffuse HGG RTK1 subtype (calibration score 0.99). Analysis of the immune transcriptome suggested a moderately high inflamed microenvironment (TIS: 8.49; percentile 70.9); Supplementary Fig. 2.D . The child received focal radiotherapy (50.4Gy) followed by nivolumab. After 5 months on immunotherapy, the child developed insulin-dependent diabetes mellitus grade 3 and hypothyroidism grade 2, both deemed immune-related. Treatment with nivolumab was not interrupted. At the time of this report, he remains on nivolumab and in complete remission 26.5 months after his original diagnosis. Table 2 Immune-related adverse events according to CTCAE v5.0 likely related to immune-checkpoint inhibitors in 6 children with RRD-HGG Adverse events (CTCAE v5.0) Grade 1 Grade 2 Grade 3 Grade 4 Total events NON-HEMATOLOGICAL Hypothyroidism 0 2 0 0 2 Hyperglycemia 0 0 1 0 1 Hypopituitarism 0 1 0 0 1 Thromboembolic event 0 1 0 0 1 Elevated AST/ALT 0 0 1 0 1 Elevated ALP 1 0 0 0 1 Elevated Cholesterol 1 0 0 0 1 HEMATOLOGICAL White blood cells decreased 1 0 0 0 1 Anemia 1 0 0 0 1 ALP: alkaline phosphatase, ALT: alanine aminotransferase, AST: aspartate aminotransferase, CTCAE: Common Terminology Criteria for Adverse Events, HGG: high grade gliomas. Discussion Whilst the use of ICI has had a limited impact across the wider range of malignant brain tumours in children, 26 there are subsets of patients for whom these represent a major breakthrough. Bouffet et al. reported the first evidence supporting the use of ICI in two siblings with CMMRD and HGG. 2 Following this experience, other authors have reported durable responses with ICI in some paediatric and young adult cases with RRD-HGG. 27 , 28 The pilot study of nivolumab in a cohort of 10 children with relapsed/refractory cancers with increased TMB and/or MMRD (NCT02992964) showed a 2-year OS of 43% for patients with malignant gliomas. 22 Those cases with higher TMB and higher MSI had longer survival, highlighting these alterations as potential predictive biomarkers. More recently, a clinical study conducted by the IRRDC reported a 5-year OS of 56% for patients with cancer treated with ICI vs 28% without ICI, showing an advantage for patients with PMS2 or MSH6 germline alterations. 3 , 17 Notwithstanding, our results and other published reports have been more disappointing. 19 , 29 Guerrini et al. evaluated anti-PD1 treatments in 8 children and adults with relapsed brain tumours, of whom 7 (88%) progressed in the first 2 months of treatment, and 6 died at a median of 5.2 months. 19 Onishi et al reported two paediatric cases, one of them treated with pembrolizumab at relapse, who progressed after three cycles of treatment. 29 The management of our study cohort was heterogeneous, which may limit the interpretation of the outcomes, but the antitumor activity of ICI was generally modest. Some particularities were identified, which may help to understand the outcomes. Interestingly, although the incidence of RRD-HGG in LS patients has been reported at around 25% of all RRD-HGG in larger cohorts, this has been relatively higher in our cohort. 20 LS patients can present RRD tumours but also replication repair-proficient tumours in childhood, which may lead to different behaviour and response to immunotherapies. 30 LS-RRD tumours acquire similar immune genomic characteristics as CMMRD patients over time, and therefore, responses to ICI are expected to be comparable. 20 , 31 However, it would be necessary larger cohorts of LS-RRD patients to assess the responses and outcomes achieved with ICI in this particular population. Three out of four of our patients (75%) were diagnosed with early disease progression at relapse and ICI were subsequently discontinued. Immune tumour flare may be difficult to distinguish from true tumour progression, which may result in premature discontinuation of treatment due to misinterpretation of radiological findings. 17 Additionally, Das et al have reported delayed responses to ICI, and a median OS of 11.6 months vs 1.2 months for those who continued with different ICI beyond progression on monotherapy (p > 0.0001). 23 These events may be considered for future trials to assess tumour responses to ICI appropriately. Immune analysis performed at progression after chemoradiation and/or single agent anti-PD1 revealed an increase in CTLA4 expression, providing evidence for the combination of anti-CTLA4 (i.e. Ipilimumab) with anti-PD1. 23 Additionally, RRD tumours enriched with RAS/MAPK pathway alterations may benefit from ICI in combination with MEK inhibitors. 23 , 32 These combinatorial strategies, as well as PD1 inhibitors in combination with other ICI and re-irradiation, should be explored to improve survival rates. 23 Prolonged survival was observed in two cases of our series. Both underwent surgical resection and radiotherapy, presented POLE mutations, and showed the highest TMB of the cohort, which have been proposed as potential predictive biomarkers. 1 , 33 Although this review is focused on RRD-HGG, it is worth noting the remarkable response to rituximab/nivolumab achieved in case #5. B-cell Lymphomas in CMMRD are rare and generally treated with conventional chemotherapy with or without rituximab, with favourable outcomes. 34 However, the use of chemotherapy-sparing treatment strategies in this population remains uncommon, and the mechanisms underlying the sustained response observed in this case are not fully understood. Given the inherent predisposition to develop other malignancies over time, minimising the exposure to certain chemotherapeutic agents, considering their potential contribution to carcinogenesis, may be relevant in these children. 35 Hence, this experience warrants further investigation and deeper molecular characterisation of these patients in future studies. Advances in the molecular analysis within the IRRDC have demonstrated that these tumours evolve in the context of their intrinsic genomic instability and the sensitivity to immunotherapy. 3 , 17 , 36 The analysis of tumour microenvironment has evidenced that higher TIS correlates with better responses to ICI. Tumours with high TMB and high TIS have shown impressive responses to ICI, with 3-year OS of 86%. 25 Additionally, three subgroups of RRD patients with different clinical and molecular features, have been described: RRD1 (MMR defects with PPD variants), RRD2 (MMR defects alone), and RRD3 (MMR defects with IDH1/2 mutations). RRD1 appears enriched with CMMRD cases, presenting higher TMB and better responses to ICI. Otherwise, the RRD3 subgroup is more frequently found in LS and is associated with lower TMB. 37 These findings highlight the importance of molecular and genomic studies and repeated biopsies at recurrence to understand the different responses achieved with ICI and guide individualised treatments and combinations. Other treatments have also been investigated in RRD-HGG. Preclinical studies in vitro and in vivo with quisinostat have shown increased tumour sensitivity and reduction in tumour burden, lending itself for potential combinations with ICI. 12 The IDH1/2 inhibitor vorasidenib has demonstrated prolonged PFS in adults with recurrent radiotherapy/chemotherapy-naive IDH -mutant low-grade gliomas compared to placebo. 38 Hence, its use in RRD-HGG with IDH1/2 mutation may be considered in future research, particularly for the RRD3 subgroup. 39 , 40 Additionally, the identification of increased levels of LAG3 and TIGIT, provides new possible targets that warrant further investigation. 25 In summary, the use of ICI in RRD-HGG is underpinned by a robust preclinical rationale and has demonstrated objective responses and survival advantage in some patients, with manageable toxicity. In contrast, our results show modest antitumor activity of ICI in a heterogeneous cohort of RRD-HGG, highlighting the need for further understanding of the strongest predictive biomarkers and the specific mechanisms of resistance to ICI. Serial biopsies at the time of relapse and cooperation with expert groups could unveil possible resistance mechanisms and genetic evolution to continue honing treatment strategies and improve survival outcomes for children with RRD-HGG. Abbreviations AE Adverse event ALP Alkaline phosphatase CMMRD Constitutional mismatch repair deficiency CT Computed tomography CTCAE Common terminology criteria for adverse events GTR Gross total resection HGG High-grade glioma ICI Immune checkpoint inhibitors IRRDC International replication repair deficiency consortium ITCC Innovative Therapies for Children and adolescents with Cancer LS Lynch syndrome MMR Mismatch repair MRI Magnetic resonance imaging MSI Microsatellite instability Mut/Mb Mutations per megabase NGS Next-generation sequencing NOS Not otherwise specified OS Overall survival PD Progressive disease PFS Progression free survival pHGG Paediatric type diffuse high-grade gliomas PPD DNA polymerases proofreading RRD Replication repair deficiency SD Stable disease TIS tumour inflammation signature TMB tumour mutational burden TYA Teenager and Young Adult WES Whole exome sequencing WHO World health organization 95% CI 95% Confidence interval Declarations Competing Interests MPS has received funding for a fellowship from the Hall-Hunter Foundation via the Royal Marsden Cancer Charity (RMCC). FC is partly funded by The Giant Pledge via the RMCC, has had a Consulting role for Ipsen UK Ltd and acknowledges funding to the Paediatric and Adolescent Neuro-Oncology and Drug Development Unit from the Hall Hunter Foundation and Courtney’s Team Marsden Fund via the RMCC. Funding MPS is funded by the Hall-Hunter Foundation via the Royal Marsden Cancer Charity (RMCC). FC is partly funded by The Giant Pledge via the RMCC and acknowledges funding to the Paediatric Neuro-Oncology and Drug Development Unit from the Hall Hunter Foundation and Courtney’s Team Marsden Fund via the RMCC. LVM is funded by the Oak Foundation via the RMCC. We acknowledge National Institute for Health Research (NIHR) Biomedical Research Centre (BRC) Funding and Experimental Cancer Medicines Centre (ECMC) funding to the Royal Marsden/Institute of Cancer Research. TJ is grateful for funding from the Brain Tumour Charity (including the EVEREST Centre (GN-000707)). Olivia Hodson Cancer Fund, Cancer Research UK and the National Institute of Health Research. All research at Great Ormond Street Hospital NHS Foundation Trust and UCL Great Ormond Street Institute of Child Health is made possible by the NIHR Great Ormond Street Hospital Biomedical Research Centre. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health. Author Contribution All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Marta Perez-Somarriba, Anna Campello and Fernando Carceller. The first draft of the manuscript was written by Marta Perez-Somarriba and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. 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Clin Cancer Res 30:3378–3387 Bagchi S, Yuan R, Engleman EG (2021) Immune Checkpoint Inhibitors for the Treatment of Cancer: Clinical Impact and Mechanisms of Response and Resistance. Annu Rev Pathol 16:223–249 Das A, Tabori U, Sambira Nahum LC et al (2023) Efficacy of nivolumab in pediatric cancers with high mutation burden and mismatch-repair deficiency. Clin Cancer Res Das A, Fernandez NR, Levine A et al (2024) Combined Immunotherapy Improves Outcome for Replication-Repair-Deficient (RRD) High-Grade Glioma Failing Anti-PD-1 Monotherapy: A Report from the International RRD Consortium. Cancer Discov 14:258–273 Geoerger B, Kang HJ, Yalon-Oren M et al (2020) Pembrolizumab in paediatric patients with advanced melanoma or a PD-L1-positive, advanced, relapsed, or refractory solid tumour or lymphoma (KEYNOTE-051): interim analysis of an open-label, single-arm, phase 1–2 trial. Lancet Oncol 21:121–133 Levine AB, Nobre L, Das A et al (2024) Immuno-oncologic profiling of pediatric brain tumors reveals major clinical significance of the tumor immune microenvironment. Nat Commun 15:5790 Dunkel IJ, Doz F, Foreman NK et al (2023) Nivolumab with or without ipilimumab in pediatric patients with high-grade CNS malignancies: Safety, efficacy, biomarker, and pharmacokinetics-CheckMate 908. Neuro Oncol 25:1530–1545 AlHarbi M, Ali Mobark N, AlMubarak L et al (2018) Durable Response to Nivolumab in a Pediatric Patient with Refractory Glioblastoma and Constitutional Biallelic Mismatch Repair Deficiency. Oncologist 23:1401–1406 Rittberg R, Harlos C, Rothenmund H et al (2021) Immune Checkpoint Inhibition as Primary Adjuvant Therapy for an IDH1-Mutant Anaplastic Astrocytoma in a Patient with CMMRD: A Case Report-Usage of Immune Checkpoint Inhibition in CMMRD. Curr Oncol 28:757–766 Onishi S, Yamasaki F, Kuraoka K et al (2023) Diagnostic and therapeutic challenges of glioblastoma as an initial malignancy of constitutional mismatch repair deficiency (CMMRD): two case reports and a literature review. BMC Med Genomics 16:6 Khandakar B, Lacy J, Gibson JA (2025) Mismatch Repair Proficient Colorectal Adenocarcinoma in Two Patients With Lynch Syndrome. Clin Genet 107:469–474 Negm L, Chung J, Nobre L et al (2025) The landscape of primary mismatch repair deficient gliomas in children, adolescents, and young adults: a multi-cohort study. Lancet Oncol 26:123–135 Campbell BB, Galati MA, Stone SC et al (2021) Mutations in the RAS/MAPK Pathway Drive Replication Repair-Deficient Hypermutated Tumors and Confer Sensitivity to MEK Inhibition. Cancer Discov 11:1454–1467 Yang C, Austin F, Richard H et al (2019) Lynch syndrome-associated ultra-hypermutated pediatric glioblastoma mimicking a constitutional mismatch repair deficiency syndrome. Cold Spring Harb Mol Case Stud 5 Rigaud C, Forster VJ, Al-Tarrah H et al (2024) Comprehensive analysis of constitutional mismatch repair deficiency-associated non-Hodgkin lymphomas in a global cohort. Pediatr Blood Cancer 71:e31302 Karran P, Offman J, Bignami M (2003) Human mismatch repair, drug-induced DNA damage, and secondary cancer. Biochimie 85:1149–1160 Palova H, Das A, Pokorna P et al (2024) Precision immuno-oncology approach for four malignant tumors in siblings with constitutional mismatch repair deficiency syndrome. NPJ Precis Oncol 8:110 Nicholas R, Fernandez A, Das A, Levine L, Negm L, Nobre V, Bianchi L, Stengs J, Chung NM, Nunes M, Edwards E, Bouffet C, Hawkins U, Tabori, HGG-26. GENOMIC AND IMMUNE ANALYSIS OF PRIMARY REPLICATION-REPAIR DEFICIENT (RRD) GLIOMAS REVEALS THREE SUBGROUPS WITH DISTINCT DRIVERS AND RESPONSE TO IMMUNOTHERAPY: AN IRRDC REPORT, Neuro-Oncology, Volume 25, Issue Supplement_1, June 2023, Page i45. https://doi.org/10.1093/neuonc/noad073.175 Mellinghoff IK, van den Bent MJ, Blumenthal DT et al (2023) Vorasidenib in IDH1- or IDH2-Mutant Low-Grade Glioma. N Engl J Med 389:589–601 Rallis KS, George AM, Wozniak AM et al (2022) Molecular Genetics and Targeted Therapies for Paediatric High-grade Glioma. Cancer Genomics Proteom 19:390–414 Miller JJ (2022) Targeting IDH-Mutant Glioma. Neurotherapeutics 19:1724–1732 Additional Declarations No competing interests reported. Supplementary Files Supplementaryfigure1.Mutationalprofile.png Supplementary Fig 1. Mutational profile from first and second tumour available from cases #2 (A) and #4 (B). Supplementaryfigure2.TISandIC.png Supplementary Fig 2. NanoString immune assay on the second tumour from case #2: (A) tumour inflammation signature (TIS) and (B) immune checkpoints; (C) TIS on the first tumour from case #4, and (D) TIS from case #6. SupplementaryTable1.Histologicalmoleculargermline.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9131402","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Case Report","associatedPublications":[],"authors":[{"id":607804037,"identity":"31fc93ec-89e2-4716-afff-31addab51993","order_by":0,"name":"Marta Perez-Somarriba","email":"","orcid":"","institution":"The Royal Marsden NHS Foundation Trust","correspondingAuthor":false,"prefix":"","firstName":"Marta","middleName":"","lastName":"Perez-Somarriba","suffix":""},{"id":607804038,"identity":"3c35b00e-b638-4605-b0da-3ed431ce72e5","order_by":1,"name":"Anna Campello","email":"","orcid":"","institution":"The Royal Marsden NHS Foundation Trust","correspondingAuthor":false,"prefix":"","firstName":"Anna","middleName":"","lastName":"Campello","suffix":""},{"id":607804039,"identity":"12858291-f030-492d-bcae-2b49c12dacff","order_by":2,"name":"Philip Benjamin","email":"","orcid":"","institution":"The Royal Marsden NHS Foundation Trust","correspondingAuthor":false,"prefix":"","firstName":"Philip","middleName":"","lastName":"Benjamin","suffix":""},{"id":607804040,"identity":"ae862fd2-9bea-4733-ab25-75a537bf125a","order_by":3,"name":"Zita Reisz","email":"","orcid":"","institution":"King’s College Hospital","correspondingAuthor":false,"prefix":"","firstName":"Zita","middleName":"","lastName":"Reisz","suffix":""},{"id":607804041,"identity":"bd35cffa-d06f-4382-a315-0d81ea99121f","order_by":4,"name":"Istvan Bodi","email":"","orcid":"","institution":"King’s College Hospital","correspondingAuthor":false,"prefix":"","firstName":"Istvan","middleName":"","lastName":"Bodi","suffix":""},{"id":607804042,"identity":"96c9fd7a-49a6-41b3-843f-594a96e40ce3","order_by":5,"name":"Safa Al-Sarraj","email":"","orcid":"","institution":"King’s College Hospital","correspondingAuthor":false,"prefix":"","firstName":"Safa","middleName":"","lastName":"Al-Sarraj","suffix":""},{"id":607804043,"identity":"e4cb4005-9d49-4765-b630-ff74fad066c9","order_by":6,"name":"Leslie R. 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Axial T1 post-contrast sequences: (A) Initial MRI scan consistent with left occipital enhancing lesion with peripheral oedema; (B) Post-operative MRI scan consistent with gross-total resection; (C) New right frontal enhancing lesion 19 months after initial diagnosis, with no evidence of recurrence at the level of the primary left occipital location; (D) Post-operative MRI scan showing gross-total resection of the right frontal lesion. Then, 25 months after initial diagnosis, the child presented with superior vena cava syndrome. Chest CT scan showed a large mediastinal mass (E, F) consistent with lymphoblastic lymphoma on histology. Thirty-five months after initial diagnosis, he presented a symptomatic recurrence: axial T1 post-contrast MRI showing two enhancing lesions in the right temporal pole and left cerebellopontine angle (G, arrows).\u003c/p\u003e\n\u003cp\u003e*The child received 26 doses in total: 22 as part of his adjuvant treatment upfront plus 4 additional doses given until completion of focal radiotherapy after first relapse. **Nivolumab/ipilimumab interrupted after 2 cycles due to thrombus in a developmental venous anomaly in the fourth ventricle associated with mild triventricular dilatation (image not shown), followed by permanent discontinuation of nivolumab/ipilimumab due to intercurrent diagnosis of lymphoblastic lymphoma.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9131402/v1/48fff48fa42b54a3eacda34f.jpg"},{"id":106475296,"identity":"7432a856-ab74-403a-8103-f00883e411cc","added_by":"auto","created_at":"2026-04-09 02:55:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1297385,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9131402/v1/ad922273-ccfc-4ede-84af-35fb568d2ab8.pdf"},{"id":104887262,"identity":"8ceac5ef-20f8-4f35-8db7-49f05552739f","added_by":"auto","created_at":"2026-03-18 10:11:24","extension":"png","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":190212,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSupplementary Fig 1.\u003c/strong\u003e Mutational profile from first and second tumour available from cases #2 (A) and #4 (B).\u003c/p\u003e","description":"","filename":"Supplementaryfigure1.Mutationalprofile.png","url":"https://assets-eu.researchsquare.com/files/rs-9131402/v1/dccafe514212c7885470e4bf.png"},{"id":104887202,"identity":"d321862e-0c28-45cd-8811-f9c8f3498e07","added_by":"auto","created_at":"2026-03-18 10:11:11","extension":"png","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":563781,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSupplementary Fig 2.\u003c/strong\u003e NanoString immune assay on the second tumour from case #2: (A) tumour inflammation signature (TIS) and (B) immune checkpoints; (C) TIS on the first tumour from case #4, and (D) TIS from case #6.\u003c/p\u003e","description":"","filename":"Supplementaryfigure2.TISandIC.png","url":"https://assets-eu.researchsquare.com/files/rs-9131402/v1/49118d2e3a7e309102d4f470.png"},{"id":104887326,"identity":"54d47e05-68ca-447f-b6a9-4cc74d0e14df","added_by":"auto","created_at":"2026-03-18 10:11:29","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":22992,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryTable1.Histologicalmoleculargermline.docx","url":"https://assets-eu.researchsquare.com/files/rs-9131402/v1/9133c25a8c6aafb968912815.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Immune checkpoint inhibitors in children with replication-repair-deficient high-grade gliomas. The South London Paediatric \u0026 TYA Neuro-Oncology Network experience","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGenetic variants in DNA mismatch repair (MMR) genes (\u003cem\u003eMLH1, MSH2, MSH6, PMS2\u003c/em\u003e) and/or DNA polymerases proofreading (PPD) genes (\u003cem\u003ePOLE, POLD1\u003c/em\u003e) cause DNA replication repair deficiencies (RRD), predisposing children to an increased lifetime risk of cancer, including brain tumours.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eBi-allelic germline mutations in MMR genes define Constitutional Mismatch Repair Deficiency (CMMRD) syndrome. Virtually all individuals with this condition will develop cancer in the first two decades of life, with a new malignancy at an average of every 2 years.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e Brain tumours are the most frequent cancer encountered, followed by haematological and gastrointestinal tumours.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eConversely, monoallelic germline MMR mutations define Lynch syndrome (LS) which predisposes to gastrointestinal and endometrial cancers in early adulthood.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Brain tumours have been sporadically described in adolescents and young adults with LS, but risk factors and prevalence remain poorly understood. In both conditions, high-grade gliomas (HGG) are the most common brain tumour.\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e,\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eReplication repair-deficient high-grade gliomas (RRD-HGG) account for 6% of all paediatric-type diffuse HGG (pHGG) and are considered a distinct subgroup genomically.\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e Histologically, are most often glioblastoma (WHO grade 4) or HGG not otherwise specified (NOS), with loss of MMR protein expression. They also display a distinctive hypomethylation pattern and cluster within a partially characterized group of HGGs previously designated \u0026ldquo;wild-type C\u0026rdquo; or \u0026ldquo;paediatric RTK1\u0026rdquo;.\u003csup\u003e5,8,9\u003c/sup\u003e These tumours exhibit high tumour mutational burden (TMB) (\u0026ge;\u0026thinsp;10 Mut/Mb), and/or microsatellite instability (MSI)\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e with even higher TMB when PPD genes are also altered.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eRRD-HGGs have been generally treated according to institutional/national HGG guidelines\u003csup\u003e\u003cspan additionalcitationids=\"CR14 CR15 CR16 CR17 CR18\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, achieving a median progression-free survival (PFS) of 9 months, and survival post-recurrence on conventional therapies less than 3 months.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eImportantly, the immunogenic nature of RRD-HGG makes these tumours more prone to respond to immunotherapies, such as immune checkpoint inhibitors (ICI).\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e,\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eClinical activity of ICI in paediatric RRD-HGG has been demonstrated by the International Replication Repair Deficiency Consortium (IRRDC), although optimal treatment regimens and timing remain undefined.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eGiven the rarity of RRD-HGG, conducting large-scale clinical trials to evaluate the best ICI of choice and/or optimal drug combinations can make it very challenging to persuade funders, industry partners, and regulators.\u003c/p\u003e \u003cp\u003eWe aim to expand the body of knowledge on the treatment of RRD-HGG with ICI based on our institutional experience to help guide future studies and therapeutic strategies.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003ePatients aged 1 to 25 years, diagnosed with RRD-HGG and receiving treatment with ICI within the South London Paediatric \u0026amp; Teenager and Young Adult Neuro-Oncology Network (SLN), which includes the Royal Marsden Hospital, St George\u0026rsquo;s Hospital and King\u0026rsquo;s College Hospital, together with The Institute of Cancer Research as academic partner, between 2019 and 2023 were eligible. Histological diagnosis was based on the 2016 or 2021 WHO classification of tumours of the central nervous system, depending on the year of diagnosis. RRD-HGG were defined based on loss expression of MMR proteins, germline MMR gene alterations, MSI and/or TMB\u0026thinsp;\u0026ge;\u0026thinsp;10 Mut/Mb.\u003c/p\u003e \u003cp\u003eClinical, radiological, histopathological, molecular and survival data were collected following approval from our institutional review board.\u003c/p\u003e \u003cp\u003eMolecular, genomic, and immune profile analysis from patients included in the IRRDC registry was added, where available.\u003c/p\u003e \u003cp\u003ePFS was defined from the first course of ICI (regardless of whether this was started at first line or relapse) to disease progression (according to RANO or iRANO criteria, where appropriate), death or last follow-up, whichever occurred earlier. Overall survival (OS) was defined from diagnosis to death or last follow-up, whichever occurred earlier.\u003c/p\u003e \u003cp\u003eAdverse events (AE) were graded according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5. Survival outcomes were calculated using the Kaplan-Meier and univariable Cox proportional hazards methods. Statistical analyses were carried out using IBM SPSS Statistics v.30.0.0.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eSix patients were identified (3 males, 3 females). Demographic, clinical, radiological, histological, molecular, therapeutic, and survival data are summarised in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and germline and molecular findings in \u003cb\u003eSupplementary Table\u0026nbsp;1\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eMedian age was 9.6 years (range 2.74\u0026ndash;11.02). Five were supratentorial (83%), and one spinal. Germline testing confirmed heterozygous \u003cem\u003eMMR\u003c/em\u003e gene variants (LS) in 4 cases (67%) and homozygous variants (CMMRD) in 2 (33%).\u003c/p\u003e \u003cp\u003eGenomic and immune profile analysis from the IRRDC was available for 3 patients #2, #4 and #6 (\u003cb\u003eSupplementary Fig.\u0026nbsp;1; Supplementary Fig.\u0026nbsp;2)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eICI were used upfront after surgery in one case with a synchronous lymphoma (#5), and upfront after surgery and radiotherapy in three cases (#2, #4, #6). ICI were used at relapse in two cases who were ICI-naive (#1, #3) and in two who had already received ICI upfront (#2, #4); Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of demographics, clinical, radiological, histological and molecular characteristics, treatment, and outcome of six children diagnosed with RRD-HGG\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eMedian age (range)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u0026thinsp;=\u0026thinsp;6\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e9.6 years (2.74\u0026ndash;11.02)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGender (F/M)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3/3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50%/50%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eClinical features/symptoms at presentation\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaf\u0026eacute;-au-lait spots\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSeizures\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeadaches\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVomiting\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHemiparesis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBack pain\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFamilial history of MMR-deficiency\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eUnderlying cancer predisposing conditions\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHomozygous deficiency (CMMRD syndrome)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeterozygous deficiency (Lynch syndrome)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGermline gene alteration\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eMLH1\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eMSH2\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eMSH6*\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003ePMS2*\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLocation\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSupratentorial\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e83%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpinal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHistology\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGlioblastoma WHO grade 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnaplastic astrocytoma WHO grade 3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePediatric High grade glioma WHO grade 4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMolecular tumor profile\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDNA replication repair protein deficits\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eMLH1\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eMSH2\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eMHS6\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003ePMS2\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003ePOLE/POLD1\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOther molecular alterations\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eIDH\u003c/em\u003e mutation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eATRX\u003c/em\u003e mutation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eTP53\u003c/em\u003e mutation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cem\u003eNRAS/MAPK\u003c/em\u003e mutation\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eOther tumors\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSynchronous tumor\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMetachronous tumor\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTreatment upfront\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurgery**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e100%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadiotherapy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemotherapy (concomitant and/or adjuvant)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e33%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAdjuvant ICI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e67%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTreatment at relapse (n\u0026thinsp;=\u0026thinsp;5)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurgery***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRadiotherapy****\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eICI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMedian PFS from first ICI\u003c/b\u003e (95%CI / range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e4.1 months (0.13\u0026ndash;8.06 / 0.6\u0026ndash;26.5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMedian OS\u003c/b\u003e (95%CI / range)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e11.1 months (10.06\u0026ndash;12.14 / 10.2\u0026ndash;35.3)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e95%CI: 95% confidence interval, CMMRD: congenital mismatch repair deficiency, F: female, HGG: high grade glioma, ICI: immune checkpoint inhibitor, M: male, MMR: mismatch repair deficiency, N/A: not available, OS: overall survival, PFS: progression-free survival, RRD: replication repair deficiency, WHO: World Health Organization.\u003c/p\u003e \u003cp\u003e*MSH6 and PMS2 mutations: one heterozygous and one homozygous, each. **Partial resection (n\u0026thinsp;=\u0026thinsp;4), subtotal resection (n\u0026thinsp;=\u0026thinsp;1), gross total resection (n\u0026thinsp;=\u0026thinsp;1). ***Biopsy, partial resection, and gross total resection (n\u0026thinsp;=\u0026thinsp;1 each). ****Re-irradiation (n\u0026thinsp;=\u0026thinsp;2), first-time radiotherapy at relapse (n\u0026thinsp;=\u0026thinsp;1).\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe median PFS and OS (95%CI; range) were 4.1 (0.13\u0026ndash;8.06; 0.6\u0026ndash;26.5) and 11.1 months (10.06\u0026ndash;12.140; 10.2\u0026ndash;35.3), respectively.\u003c/p\u003e \u003cp\u003eICI were generally well tolerated. Grade 3 toxicities included hyperglycaemia, due to new onset of insulin-dependent diabetes and elevated ALT/AST. There were no grade 4 AEs. Toxicities are summarised in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n\u003ch3\u003eCase descriptions:\u003c/h3\u003e\n\u003cp\u003eCase #1\u003c/p\u003e \u003cp\u003eA 2-year-old female was diagnosed with a left fronto-temporo-parietal glioblastoma IDH-wildtype (WHO grade 4) with \u003cem\u003ePMS2\u003c/em\u003e loss. TMB, MSI, and the immune profile were unknown. Genetic studies identified a heterozygous germline variant in the \u003cem\u003ePMS2\u003c/em\u003e gene.\u003c/p\u003e \u003cp\u003eShe underwent partial resection of the tumour followed by chemotherapy according to HIT-SKK 92 protocol. After 3.7 months, the tumour progressed, and the child was enrolled on the pembrolizumab phase I/II trial (NCT02332668) in our centre.\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e No grade3/4 AEs were reported. After 3.7 months of treatment, a routine MRI showed progressive disease. The child died 10 months after the initial diagnosis.\u003c/p\u003e \u003cp\u003eCase #2\u003c/p\u003e \u003cp\u003eAn 8-year-old male presented with a left occipital lesion. Gross total resection (GTR) was achieved. Histology confirmed HGG/glioblastoma IDH-wildtype (WHO grade 4) with \u003cem\u003eMSH6\u003c/em\u003e and \u003cem\u003ePMS2\u003c/em\u003e loss. Germline studies confirmed homozygous variants in the \u003cem\u003ePMS2\u003c/em\u003e gene. Sequencing confirmed ultra-hypermutation (TMB: 432.8 mut/Mb) with mutations in \u003cem\u003ePOLE (p.A463D, p.S459F)\u003c/em\u003e, \u003cem\u003eMLH1 and MSH6\u003c/em\u003e, \u003cem\u003eTP53, and NF1\u003c/em\u003e. He received focal radiotherapy (54Gy) with concomitant lomustine, followed by pembrolizumab. The child also received a bespoke peptide vaccine plus GM-CSF privately for 12 months, as per parental decision, whilst on adjuvant pembrolizumab.\u003c/p\u003e \u003cp\u003eNineteen months after diagnosis, a new asymptomatic right frontal lesion was found on a routine MRI scan. The lesion was completely resected and consistent with HGG (WHO grade 4). Sequencing confirmed TMB of 457.1 Mut/Mb with MMR and PPD alterations, but a non-overlapping (\u0026lt;\u0026thinsp;0.3%) mutational profile, suggesting that this was a second primary tumour rather than a relapse \u003cb\u003e(Supplementary Fig.\u0026nbsp;1.A)\u003c/b\u003e. The patient received focal radiotherapy (54Gy) followed by 4 additional cycles of pembrolizumab (total 26 cycles) whilst access to nivolumab/ipilimumab was being secured. After 2 cycles of nivolumab/ipilimumab, a routine MRI showed a thrombus within a pre-existing developmental venous anomaly in the fourth ventricle. ICI were put on hold, and the child was managed conservatively. In the meantime, the immune transcriptome analysis suggested a relatively low tumour inflammation score (TIS: 7.11 percentile 13.6) \u003cb\u003e(Supplementary Fig.\u0026nbsp;2A, 2B)\u003c/b\u003e, possibly explaining the immune-escape on pembrolizumab.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eMeanwhile, the child presented with signs of superior vena cava syndrome. A chest CT scan showed a large mediastinal mass. The biopsy confirmed lymphoblastic lymphoma (lymphocytic lineage could not be confirmed). The plan to resume immunotherapy was abandoned, and he started chemotherapy as per UKALL 2019 guidelines. The lymphoma responded, and the child entered in remission. He continued regular head MRI scans with no evidence of recurrence until 8 months after the lymphoma diagnosis, when a routine head MRI identified two dural-based lesions located in the right temporal pole and the left cerebellopontine angle.\u003c/p\u003e \u003cp\u003eThe biopsy of the right temporal lesion confirmed a pediatric-type diffuse high-grade glioma favouring RTK1 subtype on methylation (calibration score 0.99). Sequencing and analysis of mutational profiles were not possible at that time. Soon after that, the child presented an acute intratumoural bleed within the metastatic deposit in the left cerebellopontine angle. He subsequently deteriorated, requiring intubation and ventilation. After a multidisciplinary discussion limitation of further therapeutic effort were agreed with the family. The child died 36 months after the initial diagnosis \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e*The child received 26 doses in total: 22 as part of his adjuvant treatment upfront plus 4 additional doses given until completion of focal radiotherapy after first relapse. **Nivolumab/ipilimumab interrupted after 2 cycles due to thrombus in a developmental venous anomaly in the fourth ventricle associated with mild triventricular dilatation (image not shown), followed by permanent discontinuation of nivolumab/ipilimumab due to intercurrent diagnosis of lymphoblastic lymphoma.\u003c/p\u003e \u003cp\u003eCase #3\u003c/p\u003e \u003cp\u003eAn 11-year-old female was diagnosed with a left frontal glioblastoma (WHO grade 4) with \u003cem\u003eMSH6\u003c/em\u003e loss and \u003cem\u003eIDH1\u003c/em\u003e R132H mutation (not classifiable on methylation). Germline studies confirmed a heterozygous variant in the \u003cem\u003eMSH6\u003c/em\u003e gene.\u003c/p\u003e \u003cp\u003eThe child underwent a partial resection followed by focal radiotherapy (54Gy) with concomitant temozolomide and adjuvant temozolomide/lomustine. After 2 cycles, the tumour progressed.\u003c/p\u003e \u003cp\u003eThe tumour was resected and the child was transferred to our institution to receive nivolumab and lirilumab within the AcS\u0026Eacute;-eSMART trial (NCT02613962). However, she failed screening due to further local tumour progression before treatment initiation. Surgery was performed with histology in keeping with recurrent glioblastoma (molecular investigations not repeated). She was then enrolled in the pembrolizumab trial (NCT02332668).\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e After one cycle, she developed neurological symptoms. An MRI scan confirmed tumour progression, and treatment was discontinued. TMB, MSI, and immune profile were unknown. She died 11.7 months after initial diagnosis.\u003c/p\u003e \u003cp\u003eCase #4\u003c/p\u003e \u003cp\u003eA 12-year-old female with a family history of LS was diagnosed with a right parietal glioblastoma (WHO grade 4) with \u003cem\u003eMLH1\u003c/em\u003e and \u003cem\u003ePMS2\u003c/em\u003e loss (not classifiable on methylation) partially resected. Germline studies confirmed a heterozygous mutation in the \u003cem\u003eMLH1\u003c/em\u003e gene. She received focal radiotherapy (54Gy) with concomitant lomustine, followed by pembrolizumab. Sequencing demonstrated a TMB of 58 Mut/Mb, with pathogenic \u003cem\u003eTP53\u003c/em\u003e and \u003cem\u003eNF1\u003c/em\u003e variants. Analysis of the immune transcriptome suggested a moderately inflamed microenvironment (TIS: 7.96; percentile 52.4); \u003cb\u003eSupplementary Fig.\u0026nbsp;2C\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eHer disease remained stable until seven months after diagnosis, when a routine MRI scan showed a new suprasellar mass associated with new central hypoadrenalism and hypogonadotropic hypogonadism. Tumour biopsy was consistent with paediatric high-grade glioma IDH-wildtype RTK1 type (calibration score 1.0) harbouring the same pathogenic \u003cem\u003eTP53\u003c/em\u003e variant and a TMB of 56.6 Mut/Mb. However, when compared with the first tumour, \u0026lt;\u0026thinsp;10% of variants were shared between both specimens \u003cb\u003e(Supplementary Fig.\u0026nbsp;1.B)\u003c/b\u003e. She received focal radiotherapy (40Gy) followed by nivolumab. Unfortunately, after 3 cycles of nivolumab she presented clinical and radiological progression and treatment was discontinued. The patient died 11 months after initial diagnosis.\u003c/p\u003e \u003cp\u003eCase #5\u003c/p\u003e \u003cp\u003eA 10-year-old male whose brother had died due to a T-cell lymphoma was diagnosed at another European centre with an abdominal mass. A head/spine MRI scan done as part of the routine diagnostic work-up identified a synchronous frontal lesion. The patient was neurologically asymptomatic.\u003c/p\u003e \u003cp\u003eThe abdominal mass was completely resected, and a subtotal resection of the intracranial lesion was achieved. The histology confirmed an abdominal Burkitt\u0026acute;s lymphoma and an anaplastic astrocytoma (WHO grade 3) with \u003cem\u003eIDH1\u003c/em\u003e mutation (R132H) and loss of expression of \u003cem\u003eMSH2\u003c/em\u003e and \u003cem\u003eMSH6\u003c/em\u003e. Germline testing confirmed a homozygous variant in the \u003cem\u003eMSH6\u003c/em\u003e gene. Methylation, TMB, MSI, and the immune profile were not available.\u003c/p\u003e \u003cp\u003eFollowing surgery, the patient received rituximab (6 cycles) for the Burkitt\u0026acute;s lymphoma, achieving complete remission, alongside nivolumab for the HGG. No radiotherapy or chemotherapy was administered upfront. The anaplastic astrocytoma remained stable. Six months after diagnosis, an MRI scan showed tumour progression in the left hemisphere. By then, the family had relocated to the UK, and his care was transferred to our centre. He received focal radiotherapy (54Gy), but he continued to deteriorate and died 11 months after initial diagnosis.\u003c/p\u003e \u003cp\u003eCase #6\u003c/p\u003e \u003cp\u003eA 4-year-old male with a family history of LS presented with back pain and loss of sensitivity in both legs. An MRI scan identified an intraspinal lesion between T8 and T12. The lesion was partially resected. The histology was consistent with HGG (WHO grade 4) with loss of expression of \u003cem\u003eMLH1, MSH2, MSH6\u003c/em\u003e, and \u003cem\u003ePMS2\u003c/em\u003e. Germline studies confirmed a heterozygous variant in the \u003cem\u003eMSH2\u003c/em\u003e gene.\u003c/p\u003e \u003cp\u003eSequencing and WES confirmed ultra-hypermutation (TMB: 307.69 Mut/Mb) with somatic mutations in \u003cem\u003ePOLE (c.641BG\u0026thinsp;\u0026gt;\u0026thinsp;A p.Glu2140Lys)\u003c/em\u003e, \u003cem\u003eMSH2, MLH1, PMS2, TP53\u003c/em\u003e, and \u003cem\u003eNF1.\u003c/em\u003e Methylation profiling classified the tumour as paediatric-type diffuse HGG RTK1 subtype (calibration score 0.99). Analysis of the immune transcriptome suggested a moderately high inflamed microenvironment (TIS: 8.49; percentile 70.9); \u003cb\u003eSupplementary Fig.\u0026nbsp;2.D\u003c/b\u003e.\u003c/p\u003e \u003cp\u003eThe child received focal radiotherapy (50.4Gy) followed by nivolumab. After 5 months on immunotherapy, the child developed insulin-dependent diabetes mellitus grade 3 and hypothyroidism grade 2, both deemed immune-related. Treatment with nivolumab was not interrupted. At the time of this report, he remains on nivolumab and in complete remission 26.5 months after his original diagnosis.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eImmune-related adverse events according to CTCAE v5.0 likely related to immune-checkpoint inhibitors in 6 children with RRD-HGG\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAdverse events (CTCAE v5.0)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGrade 1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGrade 2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGrade 3\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGrade 4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTotal events\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eNON-HEMATOLOGICAL\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHypothyroidism\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHyperglycemia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHypopituitarism\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eThromboembolic event\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElevated AST/ALT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElevated ALP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eElevated Cholesterol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHEMATOLOGICAL\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWhite blood cells decreased\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnemia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"6\"\u003eALP: alkaline phosphatase, ALT: alanine aminotransferase, AST: aspartate aminotransferase, CTCAE: Common Terminology Criteria for Adverse Events, HGG: high grade gliomas.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eWhilst the use of ICI has had a limited impact across the wider range of malignant brain tumours in children,\u003csup\u003e26\u003c/sup\u003e there are subsets of patients for whom these represent a major breakthrough. Bouffet et al. reported the first evidence supporting the use of ICI in two siblings with CMMRD and HGG.\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e Following this experience, other authors have reported durable responses with ICI in some paediatric and young adult cases with RRD-HGG.\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe pilot study of nivolumab in a cohort of 10 children with relapsed/refractory cancers with increased TMB and/or MMRD (NCT02992964) showed a 2-year OS of 43% for patients with malignant gliomas.\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Those cases with higher TMB and higher MSI had longer survival, highlighting these alterations as potential predictive biomarkers.\u003c/p\u003e \u003cp\u003eMore recently, a clinical study conducted by the IRRDC reported a 5-year OS of 56% for patients with cancer treated with ICI vs 28% without ICI, showing an advantage for patients with \u003cem\u003ePMS2\u003c/em\u003e or \u003cem\u003eMSH6\u003c/em\u003e germline alterations.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eNotwithstanding, our results and other published reports have been more disappointing.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e Guerrini et al. evaluated anti-PD1 treatments in 8 children and adults with relapsed brain tumours, of whom 7 (88%) progressed in the first 2 months of treatment, and 6 died at a median of 5.2 months.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e Onishi et al reported two paediatric cases, one of them treated with pembrolizumab at relapse, who progressed after three cycles of treatment.\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe management of our study cohort was heterogeneous, which may limit the interpretation of the outcomes, but the antitumor activity of ICI was generally modest. Some particularities were identified, which may help to understand the outcomes.\u003c/p\u003e \u003cp\u003eInterestingly, although the incidence of RRD-HGG in LS patients has been reported at around 25% of all RRD-HGG in larger cohorts, this has been relatively higher in our cohort.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e LS patients can present RRD tumours but also replication repair-proficient tumours in childhood, which may lead to different behaviour and response to immunotherapies.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e LS-RRD tumours acquire similar immune genomic characteristics as CMMRD patients over time, and therefore, responses to ICI are expected to be comparable.\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e However, it would be necessary larger cohorts of LS-RRD patients to assess the responses and outcomes achieved with ICI in this particular population.\u003c/p\u003e \u003cp\u003eThree out of four of our patients (75%) were diagnosed with early disease progression at relapse and ICI were subsequently discontinued.\u003c/p\u003e \u003cp\u003eImmune tumour flare may be difficult to distinguish from true tumour progression, which may result in premature discontinuation of treatment due to misinterpretation of radiological findings.\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e Additionally, Das et al have reported delayed responses to ICI, and a median OS of 11.6 months vs 1.2 months for those who continued with different ICI beyond progression on monotherapy (p\u0026thinsp;\u0026gt;\u0026thinsp;0.0001).\u003csup\u003e23\u003c/sup\u003e These events may be considered for future trials to assess tumour responses to ICI appropriately.\u003c/p\u003e \u003cp\u003eImmune analysis performed at progression after chemoradiation and/or single agent anti-PD1 revealed an increase in CTLA4 expression, providing evidence for the combination of anti-CTLA4 (i.e. Ipilimumab) with anti-PD1.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAdditionally, RRD tumours enriched with RAS/MAPK pathway alterations may benefit from ICI in combination with MEK inhibitors.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThese combinatorial strategies, as well as PD1 inhibitors in combination with other ICI and re-irradiation, should be explored to improve survival rates.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eProlonged survival was observed in two cases of our series. Both underwent surgical resection and radiotherapy, presented \u003cem\u003ePOLE\u003c/em\u003e mutations, and showed the highest TMB of the cohort, which have been proposed as potential predictive biomarkers.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAlthough this review is focused on RRD-HGG, it is worth noting the remarkable response to rituximab/nivolumab achieved in case #5. B-cell Lymphomas in CMMRD are rare and generally treated with conventional chemotherapy with or without rituximab, with favourable outcomes.\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e However, the use of chemotherapy-sparing treatment strategies in this population remains uncommon, and the mechanisms underlying the sustained response observed in this case are not fully understood. Given the inherent predisposition to develop other malignancies over time, minimising the exposure to certain chemotherapeutic agents, considering their potential contribution to carcinogenesis, may be relevant in these children.\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e Hence, this experience warrants further investigation and deeper molecular characterisation of these patients in future studies.\u003c/p\u003e \u003cp\u003eAdvances in the molecular analysis within the IRRDC have demonstrated that these tumours evolve in the context of their intrinsic genomic instability and the sensitivity to immunotherapy.\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe analysis of tumour microenvironment has evidenced that higher TIS correlates with better responses to ICI. Tumours with high TMB and high TIS have shown impressive responses to ICI, with 3-year OS of 86%.\u003csup\u003e25\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAdditionally, three subgroups of RRD patients with different clinical and molecular features, have been described: RRD1 (MMR defects with PPD variants), RRD2 (MMR defects alone), and RRD3 (MMR defects with \u003cem\u003eIDH1/2\u003c/em\u003e mutations). RRD1 appears enriched with CMMRD cases, presenting higher TMB and better responses to ICI. Otherwise, the RRD3 subgroup is more frequently found in LS and is associated with lower TMB.\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThese findings highlight the importance of molecular and genomic studies and repeated biopsies at recurrence to understand the different responses achieved with ICI and guide individualised treatments and combinations.\u003c/p\u003e \u003cp\u003eOther treatments have also been investigated in RRD-HGG. Preclinical studies in vitro and in vivo with quisinostat have shown increased tumour sensitivity and reduction in tumour burden, lending itself for potential combinations with ICI.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e The \u003cem\u003eIDH1/2\u003c/em\u003e inhibitor vorasidenib has demonstrated prolonged PFS in adults with recurrent radiotherapy/chemotherapy-naive \u003cem\u003eIDH\u003c/em\u003e-mutant low-grade gliomas compared to placebo.\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e Hence, its use in RRD-HGG with \u003cem\u003eIDH1/2\u003c/em\u003e mutation may be considered in future research, particularly for the RRD3 subgroup.\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e,\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eAdditionally, the identification of increased levels of LAG3 and TIGIT, provides new possible targets that warrant further investigation.\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn summary, the use of ICI in RRD-HGG is underpinned by a robust preclinical rationale and has demonstrated objective responses and survival advantage in some patients, with manageable toxicity. In contrast, our results show modest antitumor activity of ICI in a heterogeneous cohort of RRD-HGG, highlighting the need for further understanding of the strongest predictive biomarkers and the specific mechanisms of resistance to ICI. Serial biopsies at the time of relapse and cooperation with expert groups could unveil possible resistance mechanisms and genetic evolution to continue honing treatment strategies and improve survival outcomes for children with RRD-HGG.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eAE\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eAdverse event\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eALP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eAlkaline phosphatase\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCMMRD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eConstitutional mismatch repair deficiency\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCT\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eComputed tomography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCTCAE\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eCommon terminology criteria for adverse events\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eGTR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eGross total resection\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eHGG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eHigh-grade glioma\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eICI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eImmune checkpoint inhibitors\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eIRRDC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eInternational replication repair deficiency consortium\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eITCC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eInnovative Therapies for Children and adolescents with Cancer\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eLS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLynch syndrome\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMMR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMismatch repair\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMRI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMagnetic resonance imaging\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMSI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMicrosatellite instability\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMut/Mb\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMutations per megabase\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNGS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNext-generation sequencing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eNOS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eNot otherwise specified\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eOS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eOverall survival\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eProgressive disease\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePFS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eProgression free survival\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003epHGG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePaediatric type diffuse high-grade gliomas\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePPD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eDNA polymerases proofreading\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eRRD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eReplication repair deficiency\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eSD\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eStable disease\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eTIS\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003etumour inflammation signature\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eTMB\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003etumour mutational burden\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eTYA\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eTeenager and Young Adult\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eWES\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eWhole exome sequencing\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eWHO\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eWorld health organization\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003e95% CI\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003e95% Confidence interval\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eCompeting Interests\u003c/strong\u003e \u003cp\u003eMPS has received funding for a fellowship from the Hall-Hunter Foundation via the Royal Marsden Cancer Charity (RMCC). FC is partly funded by The Giant Pledge via the RMCC, has had a Consulting role for Ipsen UK Ltd and acknowledges funding to the Paediatric and Adolescent Neuro-Oncology and Drug Development Unit from the Hall Hunter Foundation and Courtney\u0026rsquo;s Team Marsden Fund via the RMCC.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eMPS is funded by the Hall-Hunter Foundation via the Royal Marsden Cancer Charity (RMCC). FC is partly funded by The Giant Pledge via the RMCC and acknowledges funding to the Paediatric Neuro-Oncology and Drug Development Unit from the Hall Hunter Foundation and Courtney\u0026rsquo;s Team Marsden Fund via the RMCC. LVM is funded by the Oak Foundation via the RMCC. We acknowledge National Institute for Health Research (NIHR) Biomedical Research Centre (BRC) Funding and Experimental Cancer Medicines Centre (ECMC) funding to the Royal Marsden/Institute of Cancer Research.\u003c/p\u003e \u003cp\u003eTJ is grateful for funding from the Brain Tumour Charity (including the EVEREST Centre (GN-000707)). Olivia Hodson Cancer Fund, Cancer Research UK and the National Institute of Health Research. All research at Great Ormond Street Hospital NHS Foundation Trust and UCL Great Ormond Street Institute of Child Health is made possible by the NIHR Great Ormond Street Hospital Biomedical Research Centre. The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Marta Perez-Somarriba, Anna Campello and Fernando Carceller. The first draft of the manuscript was written by Marta Perez-Somarriba and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe Royal Marsden team would like to thank Bristol Myers Squibb (BMS) for providing nivolumab for a patient via their pre-approval access program after an unsolicited request from the authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eDas A, Sudhaman S, Morgenstern D et al (2022) Genomic predictors of response to PD-1 inhibition in children with germline DNA replication repair deficiency. Nat Med 28:125\u0026ndash;135\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBouffet E, Larouche V, Campbell BB et al (2016) Immune Checkpoint Inhibition for Hypermutant Glioblastoma Multiforme Resulting From Germline Biallelic Mismatch Repair Deficiency. J Clin Oncol 34:2206\u0026ndash;2211\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eErcan AB, Aronson M, Fernandez NR et al (2024) Clinical and biological landscape of constitutional mismatch-repair deficiency syndrome: an International Replication Repair Deficiency Consortium cohort study. Lancet Oncol\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim H, Lim KY, Park JW et al (2022) Sporadic and Lynch syndrome-associated mismatch repair-deficient brain tumors. Lab Invest 102:160\u0026ndash;171\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBakry D, Aronson M, Durno C et al (2014) Genetic and clinical determinants of constitutional mismatch repair deficiency syndrome: report from the constitutional mismatch repair deficiency consortium. Eur J Cancer 50:987\u0026ndash;996\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDurno C, Ercan AB, Bianchi V et al (2021) Survival Benefit for Individuals With Constitutional Mismatch Repair Deficiency Undergoing Surveillance. J Clin Oncol 39:2779\u0026ndash;2790\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJohnson A, Severson E, Gay L et al (2017) Comprehensive Genomic Profiling of 282 Pediatric Low- and High-Grade Gliomas Reveals Genomic Drivers, Tumor Mutational Burden, and Hypermutation Signatures. Oncologist 22:1478\u0026ndash;1490\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlmuhaisen G, Alhalaseh Y, Mansour R et al (2021) Frequency of mismatch repair protein deficiency and PD-L1 in high-grade gliomas in adolescents and young adults (AYA). Brain Tumor Pathol 38:14\u0026ndash;22\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDodgshun AJ, Fukuoka K, Edwards M et al (2020) Germline-driven replication repair-deficient high-grade gliomas exhibit unique hypomethylation patterns. Acta Neuropathol 140:765\u0026ndash;776\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChung J, Negm L, Bianchi V et al (2023) Genomic Microsatellite Signatures Identify Germline Mismatch Repair Deficiency and Risk of Cancer Onset. J Clin Oncol 41:766\u0026ndash;777\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMackay A, Burford A, Molinari V et al Molecular, Pathological, Radiological, and Immune Profiling of Non-brainstem Pediatric High-Grade Glioma from the HERBY Phase II Randomized Trial. Cancer Cell 33:829\u0026ndash;842 e5, 2018\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNoll A, Myers C, Biery MC et al (2023) Therapeutic HDAC inhibition in hypermutant diffuse intrinsic pontine glioma. Neoplasia 43:100921\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStupp R, Mason WP, van den Bent MJ et al (2005) Radiotherapy plus concomitant and adjuvant temozolomide for glioblastoma. N Engl J Med 352:987\u0026ndash;996\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuerra-Garcia P, Marshall LV, Cockle JV et al (2020) Challenging the indiscriminate use of temozolomide in pediatric high-grade gliomas: A review of past, current, and emerging therapies. Pediatr Blood Cancer 67:e28011\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDaniel P, Sabri S, Chaddad A et al (2019) Temozolomide Induced Hypermutation in Glioma: Evolutionary Mechanisms and Therapeutic Opportunities. Front Oncol 9:41\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTouat M, Li YY, Boynton AN et al (2020) Mechanisms and therapeutic implications of hypermutation in gliomas. Nature 580:517\u0026ndash;523\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDas A, Ercan AB, Tabori U (2024) An update on central nervous system tumors in germline replication-repair deficiency syndromes. Neurooncol Adv 6:vdae102\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcCord M, Bartom E, Burdett K et al (2022) Modeling Therapy-Driven Evolution of Glioblastoma with Patient-Derived Xenografts. Cancers (Basel) 14\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuerrini-Rousseau L, Varlet P, Colas C et al (2019) Constitutional mismatch repair deficiency-associated brain tumors: report from the European C4CMMRD consortium. Neurooncol Adv 1:vdz033\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDas A, MacFarland SP, Meade J et al (2024) Clinical Updates and Surveillance Recommendations for DNA Replication Repair Deficiency Syndromes in Children and Young Adults. Clin Cancer Res 30:3378\u0026ndash;3387\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBagchi S, Yuan R, Engleman EG (2021) Immune Checkpoint Inhibitors for the Treatment of Cancer: Clinical Impact and Mechanisms of Response and Resistance. Annu Rev Pathol 16:223\u0026ndash;249\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDas A, Tabori U, Sambira Nahum LC et al (2023) Efficacy of nivolumab in pediatric cancers with high mutation burden and mismatch-repair deficiency. Clin Cancer Res\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDas A, Fernandez NR, Levine A et al (2024) Combined Immunotherapy Improves Outcome for Replication-Repair-Deficient (RRD) High-Grade Glioma Failing Anti-PD-1 Monotherapy: A Report from the International RRD Consortium. Cancer Discov 14:258\u0026ndash;273\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGeoerger B, Kang HJ, Yalon-Oren M et al (2020) Pembrolizumab in paediatric patients with advanced melanoma or a PD-L1-positive, advanced, relapsed, or refractory solid tumour or lymphoma (KEYNOTE-051): interim analysis of an open-label, single-arm, phase 1\u0026ndash;2 trial. Lancet Oncol 21:121\u0026ndash;133\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLevine AB, Nobre L, Das A et al (2024) Immuno-oncologic profiling of pediatric brain tumors reveals major clinical significance of the tumor immune microenvironment. Nat Commun 15:5790\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDunkel IJ, Doz F, Foreman NK et al (2023) Nivolumab with or without ipilimumab in pediatric patients with high-grade CNS malignancies: Safety, efficacy, biomarker, and pharmacokinetics-CheckMate 908. Neuro Oncol 25:1530\u0026ndash;1545\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlHarbi M, Ali Mobark N, AlMubarak L et al (2018) Durable Response to Nivolumab in a Pediatric Patient with Refractory Glioblastoma and Constitutional Biallelic Mismatch Repair Deficiency. Oncologist 23:1401\u0026ndash;1406\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRittberg R, Harlos C, Rothenmund H et al (2021) Immune Checkpoint Inhibition as Primary Adjuvant Therapy for an IDH1-Mutant Anaplastic Astrocytoma in a Patient with CMMRD: A Case Report-Usage of Immune Checkpoint Inhibition in CMMRD. Curr Oncol 28:757\u0026ndash;766\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOnishi S, Yamasaki F, Kuraoka K et al (2023) Diagnostic and therapeutic challenges of glioblastoma as an initial malignancy of constitutional mismatch repair deficiency (CMMRD): two case reports and a literature review. BMC Med Genomics 16:6\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhandakar B, Lacy J, Gibson JA (2025) Mismatch Repair Proficient Colorectal Adenocarcinoma in Two Patients With Lynch Syndrome. Clin Genet 107:469\u0026ndash;474\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNegm L, Chung J, Nobre L et al (2025) The landscape of primary mismatch repair deficient gliomas in children, adolescents, and young adults: a multi-cohort study. Lancet Oncol 26:123\u0026ndash;135\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCampbell BB, Galati MA, Stone SC et al (2021) Mutations in the RAS/MAPK Pathway Drive Replication Repair-Deficient Hypermutated Tumors and Confer Sensitivity to MEK Inhibition. Cancer Discov 11:1454\u0026ndash;1467\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang C, Austin F, Richard H et al (2019) Lynch syndrome-associated ultra-hypermutated pediatric glioblastoma mimicking a constitutional mismatch repair deficiency syndrome. Cold Spring Harb Mol Case Stud 5\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRigaud C, Forster VJ, Al-Tarrah H et al (2024) Comprehensive analysis of constitutional mismatch repair deficiency-associated non-Hodgkin lymphomas in a global cohort. Pediatr Blood Cancer 71:e31302\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKarran P, Offman J, Bignami M (2003) Human mismatch repair, drug-induced DNA damage, and secondary cancer. Biochimie 85:1149\u0026ndash;1160\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePalova H, Das A, Pokorna P et al (2024) Precision immuno-oncology approach for four malignant tumors in siblings with constitutional mismatch repair deficiency syndrome. NPJ Precis Oncol 8:110\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNicholas R, Fernandez A, Das A, Levine L, Negm L, Nobre V, Bianchi L, Stengs J, Chung NM, Nunes M, Edwards E, Bouffet C, Hawkins U, Tabori, HGG-26. GENOMIC AND IMMUNE ANALYSIS OF PRIMARY REPLICATION-REPAIR DEFICIENT (RRD) GLIOMAS REVEALS THREE SUBGROUPS WITH DISTINCT DRIVERS AND RESPONSE TO IMMUNOTHERAPY: AN IRRDC REPORT, Neuro-Oncology, Volume 25, Issue Supplement_1, June 2023, Page i45. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1093/neuonc/noad073.175\u003c/span\u003e\u003cspan address=\"10.1093/neuonc/noad073.175\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMellinghoff IK, van den Bent MJ, Blumenthal DT et al (2023) Vorasidenib in IDH1- or IDH2-Mutant Low-Grade Glioma. N Engl J Med 389:589\u0026ndash;601\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRallis KS, George AM, Wozniak AM et al (2022) Molecular Genetics and Targeted Therapies for Paediatric High-grade Glioma. Cancer Genomics Proteom 19:390\u0026ndash;414\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMiller JJ (2022) Targeting IDH-Mutant Glioma. Neurotherapeutics 19:1724\u0026ndash;1732\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Replication-repair high-grade gliomas, Immune checkpoint inhibitors, survival, biomarkers","lastPublishedDoi":"10.21203/rs.3.rs-9131402/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9131402/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003ePurpose\u003c/h2\u003e \u003cp\u003eHigh-grade gliomas (HGG) are the most common intracranial tumors in children with replication repair deficiency (RRD) syndromes. Defective DNA repair leads to a high mutational burden, providing biological rationale for immune checkpoint inhibitors (ICI). However, responses to ICI are heterogeneous, and resistance mechanisms remain poorly understood. We report on the experience of the Paediatric \u0026amp; TYA Neuro-Oncology South London Network (SLN) and collaborators on the safety and efficacy of ICI in RRD-HGG.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eClinical, histopathological, molecular, and survival data were collected from children with molecularly confirmed RRD-HGG treated with ICI at SLN between 2019\u0026ndash;2023. Descriptive statistics were used for demographics. Survival outcomes were analyzed using Kaplan-Meier estimates and univariable Cox proportional hazards models.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eSix patients were identified (Lynch syndrome n\u0026thinsp;=\u0026thinsp;4,constitutional mismatch repair deficiency n\u0026thinsp;=\u0026thinsp;2). Median age 9.6 years (range 2.74\u0026ndash;11.02). ICI was administered upfront, at relapse, or at both stages (n\u0026thinsp;=\u0026thinsp;2 each). No grade 4\u0026ndash;5 toxicities were observed. Two patients treated upfront achieved sustained responses of 14 and 26.5 months, with one remaining in complete remission at last follow-up. Median progression-free survival from first ICI exposure was 4.1 months (95% CI 0.13\u0026ndash;8.06; range 0.6\u0026ndash;26.5), and median overall survival was 11.1 months (95% CI 10.06\u0026ndash;12.14; range 10.2\u0026ndash;35.3).\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eICI use in RRD-HGG is biologically justified, but optimal agents, combinations, and predictive biomarkers need yet to be fully determined. Given the rarity of RRD-HGG, international collaborations, such as the International Replication Repair Deficiency Consortium (IRRDC), are essential to advance treatment strategies for these patients.\u003c/p\u003e","manuscriptTitle":"Immune checkpoint inhibitors in children with replication-repair-deficient high-grade gliomas. The South London Paediatric \u0026amp; TYA Neuro-Oncology Network experience","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-18 10:08:22","doi":"10.21203/rs.3.rs-9131402/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"0bc3f9e2-be7f-4471-8388-790f9fb47d88","owner":[],"postedDate":"March 18th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-09T02:54:53+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-18 10:08:22","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9131402","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9131402","identity":"rs-9131402","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}