Management of Refractory Malignancy-Associated Hemophagocytic Lymphohistiocytosis in Pediatric Patients: A Case Series of Novel Therapeutics and Treatment Challenges

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal syndrome of immune dysregulation that has primary and secondary forms. HLH is classified based on underlying triggers of malignancy, infections, and/or autoimmune processes. Primary-HLH has a genetic etiology related to defects in cytotoxic T and NK cells. The established standard of care is dexamethasone and etoposide but no guidelines exist for refractory HLH or cases triggered by malignancy. [1] We describe three pediatric patients with malignancy-associated HLH (m-HLH) to discuss complexities in initial diagnostic considerations, balance of therapeutic regimens/toxicities, and novel uses of emapalumab and ruxolitinib in refractory disease patients. Management of Refractory Malignancy-Associated Hemophagocytic Lymphohistiocytosis in Pediatric Pa- tients: A Case Series of Novel Therapeutics and Treatment Challenges Meha Krishnareddigari, UCLA, Kenny Vo, MD, UC Irvine, Arun Panigrahi, MD, UC Davis

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal syndrome of immune dysregu- lation that has primary and secondary forms. HLH is classified based on underlying triggers of malignancy, infections, and/or autoimmune processes. Primary-HLH has a genetic etiology related to defects in cytotoxic T and NK cells. The established standard of care is dexamethasone and etoposide but no guidelines exist for refractory HLH or cases triggered by malignancy. [1] We describe three pediatric patients with malignancy- associated HLH (m-HLH) to discuss complexities in initial diagnostic considerations, balance of therapeutic regimens/toxicities, and novel uses of emapalumab and ruxolitinib in refractory disease patients.

Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of dysregulation of cell death leading to a hy- perinflammatory state. HLH is categorized into primary and secondary forms. Primary, or familial HLH, is associated with known genetic mutations related to T and NK cell defects. Secondary HLH is an acquired form that is most often triggered by infection or malignancy (m-HLH) in the pediatric population. In the context of m-HLH in pediatric patients, the initial presentation presents a diagnostic conundrum. The HLH-2004 diagnostic criteria include clinical features of fever, splenomegaly, and cytopenia that overlap with common malignancies of leukemia and lymphoma. [1] There are also similarities in treatment guidelines with the use of dexamethasone and etoposide. Patients are often critically ill at presentation, which may prevent opportunities to carry out thorough diagnostic processes prior to treatment. This may lead to delays in the diagnosis and treatment of underlying malignancy. The Histiocyte Society recommends consideration 1 Posted on 4 Jan 2025 — The copyright holder is the author/funder. All rights reserved. No reuse without permission. — https://doi.org/10.22541/au.173599410.06496449/v1 — This is a preprint and has not been peer-reviewed. Data may be preliminary. of evaluation for malignancy for any patient suspected with HLH, but there are currently no established guidelines in pediatric patients to address the initial diagnostic workup, the primary treatment focus (HLH or malignancy), and the considerations for alterations of treatment regimens with respect to the toxicities of chemotherapeutic agents. [2] We now discuss 3 patients with varying presentations of m-HLH in severity, response, treatment considera- tions, and overall outcome to demonstrate the spectrum of this hyperinflammatory syndrome. Patient cases Patient 1: A 19-year-old Hispanic male with a history of asthma presented with Hodgkin’s lymphoma and treated per Children’s Oncology Group (COG) protocol AHOD1331. His course was complicated by EBV-associated HLH, presenting with splenomegaly, elevated ferritin levels exceeding 20,000 ng/mL, low NK cell activ- ity, and high fevers. Initial treatment included high-dose dexamethasone, etoposide, and anakinra, which stabilized his inflammatory markers. However, due to persistent inflammation and tachycardia, he was tran- sitioned to ruxolitinib (JAK 1/2 inhibitor) and anakinra as an outpatient. This therapy led to significant down-trending of ferritin levels, stabilizing around 1,600 ng/mL, and improvements in systemic symptoms. Despite the challenges of his treatment, including severe neutropenia and thrombocytopenia, the patient completed therapy for Hodgkin’s Lymphoma and remains in remission. His m-HLH, which was managed as an outpatient primarily with ruxolitinib, is also in remission and he is not currently receiving any therapy. Patient 2: A 16-year-old Hispanic female with persistent NK/T-cell lymphoma of the nasopharynx presented in septic shock with pancytopenia and disseminated intravascular coagulation. Initial diagnostic considera- tions included progressive lymphoma, bacteremia, and EBV viremia. HLH was a consideration, but she did not meet criteria until hospital day 7. Treatment with dexamethasone, etoposide, and rituximab showed minimal effect. With the lack of response to induction therapy, there was concern for her lymphoma as the initial driver of her HLH. A bone marrow biopsy showed evidence of NK/T-cell lymphoma. Gemcitabine and oxaliplatin were started, but she developed acute decompensation with hemodynamic instability and multi-organ system failure in response to fulminant EBV viremia. Her systemic inflammation worsened as evidenced by rises in ferritin, sIL-2 receptor, and CXCL9 (IFN γ biomarker). [3] Her elevated sIL-2 to ferritin ratio of 35:1 was consistent with studies showing correlation between lymphoma and HLH. [4] We held treatment for her lymphoma to reduce toxicities and better manage her HLH. With continued clinical deterioration, compassionate use of emapalumab, an IFNγ inhibitor indicated in primary HLH, led to damp- ening of her systemic inflammatory processes with resolution of fevers, decreased inflammatory markers, and signs of recovery of her hepatobiliary, renal, and gastrointestinal systems. [5] Unfortunately, despite demonstrating response to emapalumab, patient 2 developed fulminant candidiasis and intraparenchymal hemorrhage which she ultimately succumbed to. Patient 3: A 17-year-old Caucasian male presented with pancytopenia and proctitis and was diagnosed with T-ALL and treated per COG-AALL1231. [6] His course was complicated by bacteremia, fungemia, severe myelo- suppression, and persistent fevers. He ultimately met HLH criteria and was treated per HLH-2004. Due to his myelosuppression, adjustments were made to both his chemotherapy and his HLH treatment. Reduced doses of dexamethasone were used, and etoposide was not introduced initially. Trials of IVIG and hydro- cortisone showed minimal response. We then trialed ruxolitinib, a JAK 1/2 inhibitor shown to improve the inflammatory status of patients with HLH. [8] Although laboratory markers did not indicate resolution of his HLH, while our patient was on ruxolitinib, he had an overall improved quality of life. He had more energy, improved wound healing, and significantly fewer admissions for flares for 3 months. Abdominal imaging demonstrated diffuse hepatic fungal microabscesses confirmed with biopsy. He was previously treated with courses of voriconazole and micafungin, but doses were adjusted due to incompatibility with chemotherapy and concurrent toxicities. Treatment with a course of high dose fluconazole and repeat imaging showed res- olution of the hepatic nodules. For his HLH, we trialed a course of etoposide, which was not used before due 2 Posted on 4 Jan 2025 — The copyright holder is the author/funder. All rights reserved. No reuse without permission. — https://doi.org/10.22541/au.173599410.06496449/v1 — This is a preprint and has not been peer-reviewed. Data may be preliminary. to his myelosuppression, but HLH did not improve. With our patient’s fungal infection controlled, we began a trial of emapalumab which lasted approximately three months and resulted in progressive improvement of his inflammation, which has allowed for progression of his treatment for his T-ALL. Currently, his HLH and T-ALL both remain in remission and he has completed maintenance therapy for his leukemia.

These cases highlight the intricacies of the management of m-HLH in pediatric patients with the spectrum of disease severity and complex diagnostic evaluations one must consider at presentation. Careful consideration must be taken with suspicion of HLH to carry out a thorough workup that will prevent delays in diagnosis for possible underlying malignancy. The treatment of m-HLH is a delicate balance due to the myriad of toxicities that arise from HLH and malignancy protocols. Although they are the backbone of HLH treatment, dexamethasone and etoposide may be inappropriate for some of the more unstable patients. This also highlights the importance of recognizing a lack of response to standard treatment to explore the use of investigational therapeutics for refractory cases in a timely manner. There is much to explore and learn from the use of novel therapeutics as with our patients who received emapalumab for their refractory HLH. Although they both demonstrated response to the addition of emapalumab, one of our patients may have succumbed to fulminant candidiasis as result of emapalumab. We theorize that as emapalumab blocks IFN γ, subsequently blocking neutrophil activation and IL-6 modulation, it led to our patient being more susceptible to systemic candidiasis, resulting in fungal emboli that led to her intraparenchymal hemorrhage. [8] Both ruxolitinib and emapalumab showed promising effects in patients, but present safety concerns. In particular, the use of emapalumab, which blocks IFN γ, may lead to increased susceptibility to infections such as systemic candidiasis, potentially contributing to adverse outcomes. [9] Due to the toxicity of treatment options for concurrent processes of malignancy, infection, and HLH, novel therapeutics such as emapalumab and ruxolitinib are required and should be evaluated in larger studies. Considerations for the diagnostic approach of m-HLH should account for significant correlations like those seen in lymphoma-associated HLH and the sIL-2 to ferritin ratio. Furthermore, guidelines for the manage- ment of pediatric m-HLH are required with inclusion of adjustments to standard therapy based on toxicity, inciting factors, concurrent processes, and incorporation of novel therapeutics to lead to improved outcomes. 3 Posted on 4 Jan 2025 — The copyright holder is the author/funder. All rights reserved. No reuse without permission. — https://doi.org/10.22541/au.173599410.06496449/v1 — This is a preprint and has not been peer-reviewed. Data may be preliminary. * Value not obtained ** Patient expired Works cited [1] Henter JI, Horne A, Aric´ o M, Egeler RM, Filipovich AH, Imashuku S, Ladisch S, McClain K, Webb D, Winiarski J, Janka G. HLH-2004: Diagnostic and therapeutic guidelines for hemophagocytic lymphohistio- cytosis. Pediatr Blood Cancer. 2007 Feb;48(2):124-31. doi: 10.1002/pbc.21039. PMID: 16937360. [2] Lehmberg K, Nichols KE, Henter JI, et al. Consensus recommendations for the diagnosis and management of hemophagocytic lymphohistiocytosis associated with malignancies. Haematologica. 2015;100(8):997-1004. doi:10.3324/haematol.2015.123562 [3] Bracaglia C, Marafon DP, Caiello I, et al. High levels of interferon-gamma (IFNγ) in macrophage activation syndrome (MAS) and CXCL9 levels as a biomarker for IFNγ production in MAS. Pediatr Rheumatol Online J. 2015;13(Suppl 1):O84. Published 2015 Sep 28. doi:10.1186/1546-0096-13-S1-O84 [4] Tabata C, Tabata R. Possible prediction of underlying lymphoma by high sIL-2R/ferritin ratio in hemophagocytic syndrome. Ann Hematol. 2012 Jan;91(1):63-71. doi: 10.1007/s00277-011-1239-7. Epub 2011 Apr 27. PMID: 21523380. [5] Locatelli F, Jordan MB, Allen C, Cesaro S, Rizzari C, Rao A, Degar B, Garrington TP, Sevilla J, Putti MC, Fagioli F, Ahlmann M, Dapena Diaz JL, Henry M, De Benedetti F, Grom A, Lapeyre G, Jacqmin P, Ballabio M, de Min C. Emapalumab in Children with Primary Hemophagocytic Lymphohistiocytosis. N Engl J Med. 2020 May 7;382(19):1811-1822. doi: 10.1056/NEJMoa1911326. PMID: 32374962. [6] AALL1231: A Phase III Randomized Trial Investigating Bortezomib on a Modified Augmented BFM (ABFM) Backbone in Newly Diagnosed T- Lymphoblastic Leukemia (T-ALL) and T- Lymphoblastic Lym- phoma (T-LLy) [7] AALL1732: A Phase 3 Randomized Trial of Inotuzumab Ozogamicin for Newly Diagnosed High-Risk B-ALL; Risk Adapted Post-Induction Therapy for High-Risk B-ALL, Mixed Phenotype Acute Leukemia, and Disseminated B-LLy [8] Wang J, Wang Y, Wu L, et al. Ruxolitinib for refractory/relapsed hemophagocytic lymphohistiocytosis. Haematologica. 2020;105(5):e210-e212. doi:10.3324/haematol.2019.222471 [9] van Enckevort FH, Netea MG, Hermus AR, Sweep CG, Meis JF, Van der Meer JW, Kullberg BJ. Increased susceptibility to systemic candidiasis in interleukin-6 deficient mice. Med Mycol. 1999 Dec;37(6):419-26. doi: 10.1046/j.1365-280x.1999.00247.x. PMID: 10647123. 4