New histopathological and molecular findings in gynecological cancers.

Ovarian sex cord–stromal tumors is one area of pathology where significant advances have been made in recent years, especially in elucidation of the underlying molecular events. Sex cord–stromal tumors represent an uncommon and heterogeneous group of neoplasms that, when they exhibit classical morphology, are relatively easy to diagnose. However, there may be considerable morphological overlap between the different tumor types, and immunohistochemistry, while useful in confirming a sex cord–stromal tumor, is of minimal value in distinguishing between the different tumor types. Recent significant advances regarding molecular events (Table  1 ) include the demonstration that adult granulosa cell tumors contain somatic FOXL2 mutations in well over 90% of cases, 86 , 87 , 88 , 89 while a very large percentage of moderately and poorly differentiated Sertoli–Leydig cell tumors (SLCTs) contain DICER1 mutations; these may be somatic or germline, the latter signifying DICER1 syndrome. 88 , 89 , 90 It has also been demonstrated that well‐differentiated SLCTs represent a fundamentally different tumor type to moderately and poorly differentiated and is not associated with DICER1 variants. 91 Other studies have elucidated the molecular events in several other tumor types within the sex cord–stromal category. For example, a microcystic stromal tumor contains CTNNB1 or less frequently APC mutations and is occasionally an extracolonic manifestation of familial adenomatous polyposis, 92 , 93 while a sclerosing stromal tumor is associated with FHL2:: GLI2 fusions. 94 In problematic cases, demonstration of the appropriate molecular abnormality assists in tumor classification. Molecular events in ovarian sex cord–stromal tumors and other uncommon adnexal or para‐adnexal neoplasms. DICER1 variants (except well‐differentiated SLCT) FOXL2 variants in some tumors in older patients Abbreviations: AGCT, adult granulosa cell tumor; JGCT, juvenile granulosa cell tumor; MST (microcystic stromal tumor); SCCOHT, small cell carcinoma of the ovary of hypercalcemic type; SCTAT, sex cord tumor with annular tubules; SLCT, Sertoli Leydig cell tumor. Small cell carcinoma of the ovary of hypercalcemic type (SCCOHT), which is included in the category of miscellaneous ovarian neoplasms in WHO 2020, has been shown to be characterized by deleterious germline or somatic mutations in a single gene SMARCA4 95 , 96 , 97 in well over 90% of cases. SMARCA4 is part of the SWI/SNF complex, which is implicated in the pathogenesis of a growing number of malignancies. 98 Demonstration of this mutation and/or loss of immunohistochemical staining with SMARCA4 (BRG1) antibody may, in the correct morphological context, be crucial in the diagnosis of this highly aggressive neoplasm. 99 , 100 , 101 It is recommended that all patients diagnosed with SCCOHT should be referred for germline SMARCA4 mutation testing. 102 When diagnosing some of these uncommon neoplasms, the pathologist should raise the possibility of a germline mutation, for example DICER1 in SLCT or SMARCA4 in SCCOHT and recommend genetic referral and germline testing. It is also worth noting that given the rarity of some of these neoplasms and the overlap in morphology between them, many will benefit from referral for a specialist opinion which, as well as hopefully ensuring a correct diagnosis, facilitates the accrual of case series. 103

As early as 1983, Bokhman proposed that there were two types of endometrial carcinoma, type I and type II. 2 Broadly speaking, type I carcinomas (prototypically endometrioid‐type) arise in perimenopausal or early postmenopausal women, are low‐grade, typically early‐stage neoplasms arising on a background of atypical hyperplasia and are positive with hormone receptors. Type II carcinomas (prototypically serous‐type) arise in elderly postmenopausal women, are high‐grade, typically advanced‐stage neoplasms arising in atrophic endometrium, and are negative with hormone receptors. However, although useful as a broad concept, it was always clear that there is significant overlap in the clinical and pathological features in many individual tumors and the Bokhman classification never gained widespread acceptance among pathologists and was never used in pathological reporting. The current 2020 WHO Classification of endometrial carcinomas, 1 like prior classifications, is based on morphology. In practice, pathologists often use immunohistochemical markers to assist in classifying problematic neoplasms. However, especially with “high‐grade” endometrial carcinomas (serous, clear cell, grade 3 endometrioid, mixed, undifferentiated/dedifferentiated carcinoma and carcinosarcoma), but not exclusively, there is significant inter‐observer variation even among expert gynecological pathologists. 3 For example, in one study, three gynecological pathologists examined 56 endometrial carcinomas previously diagnosed as high‐grade and in 20 of 56 (35.8%) there was a major disagreement, including no consensus regarding the tumor type or even whether a component of high‐grade carcinoma was present. 3 In 2013, the seminal TCGA study of 373 endometrial carcinomas was published; the study only included endometrioid, serous, and mixed endometrioid and serous carcinomas with no other high‐grade carcinomas and employed a variety of modalities, including exome sequencing, somatic copy number alteration, whole genome sequencing, mRNA expression, protein expression, microRNA expression, and DNA methylation. 4 The study for the first time revealed that endometrial carcinoma consists of four intrinsic molecular types: POLE mutated ( POLE mut)/ultramutated; mismatch repair (MMR) deficient (MMRd)/microsatellite instability‐high (MSI‐H)/hypermutated; p53 abnormal (p53abn)/copy number high; and copy number low/no specific molecular profile (NSMP). It was demonstrated that the four molecular types are of prognostic significance and this has been confirmed in multiple subsequent studies with POLE mut tumors having the best prognosis (even though they are often high‐grade and sometimes exhibit substantial lymphovascular space invasion [LVSI], parameters that would typically result in adjuvant treatment) and p53abn the worst, with the other two groups having an intermediate prognosis. 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 These molecular groups also form the basis for personalized treatment of endometrial carcinomas based on the molecular classification, for example, de‐escalation of treatment in POLE mut tumors, immune checkpoint inhibitors in MMRd and POLE mut neoplasms, and chemotherapy in p53abn, while in NSMP tumors, which are hormone receptor positive, hormonal therapy may be an option. 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 Importantly, studies have shown that TCGA classification also has prognostic and predictive significance in other endometrial carcinomas, such as carcinosarcoma, clear cell carcinoma, undifferentiated/dedifferentiated carcinoma, and neuroendocrine carcinoma. 17 , 18 , 19 In a recent population‐based study, the percentages within the different TCGA groups were as follows: POLE mut 7.3%; MMRd 24%; p53abn 23.7%; and NSMP 45%. 20 Of the tumors, 6.5% were “multiple‐classifiers” reflecting the fact that POLE mut or MMRd endometrial carcinomas may exhibit secondary mutations, for example in TP53 , due to their ultramutated or hypermutated phenotype. Studies have shown that these neoplasms should be assigned to the molecular group with the best outcome. 21 , 22 Since the original TCGA publication, there has been extensive debate about how best to incorporate full molecular testing or a surrogate of this into the routine reporting of endometrial carcinomas and whether molecular classification is required in all cases. TCGA Classification has been incorporated into various international guidelines including the ESGO/ESTRO/ESP guidelines, 23 the 2020 WHO Classification, 1 and the International Federation of Gynecology and Obstetrics (FIGO) 2023 endometrial carcinoma staging system. 24 While molecular classification can be performed solely by molecular testing using next‐generation sequencing (NGS) panels, which include POLE , TP53 , and MSI analyses, a simplified surrogate classifier, referred to as the ProMisE (Proactive Molecular Risk Classifier for Endometrial Cancer) classifier, is also widely used. 6 , 8 , 9 , 12 This requires MMR protein and p53 immunohistochemical staining as well as targeted POLE molecular testing (Figure  1 ). Surrogate ProMisE (Proactive Molecular Risk Classifier for Endometrial Cancer) Classifier for molecular classification of all endometrial carcinomas (regardless of histological type). Molecular classification can be performed on biopsy or resection material. The advantage of performing on biopsy specimens is that they are typically better fixed and often comprise a relatively pure tumor population providing higher‐quality material for immunohistochemistry and molecular testing. Immunohistochemistry and NGS analyses are affected by poor fixation and, as a result, are often less than optimal in hysterectomy specimens. Another advantage of performing all the testing on biopsies is that surgical management can potentially be tailored if the molecular group is known preoperatively. A final advantage of testing biopsies is that all the histological, immunohistochemical and molecular studies are available when reporting the hysterectomy specimen, allowing for a comprehensive integrated report. This facilitates prompt decision‐making regarding adjuvant treatment at tumor board meetings. The absence of a surrogate immunohistochemical marker for predicting POLE mutations necessitates molecular testing for TCGA classification. This results in increased costs and potentially turnaround time, and many institutions do not have ready access to POLE testing. Molecular classification does not typically change therapeutic approaches in advanced‐stage (III/IV) patients, so POLE testing may not be needed; however, even in these cases, the presence of a POLE mutation may be indicative of an improved prognosis or response to immunotherapy and a potentially “salvageable” neoplasm and is useful information for the patient. There is a significant group of endometrial carcinomas (grade 1/2 endometrioid, MMR proficient, p53 wild‐type, stage IA, estrogen receptor (ER) positive, no substantial LVSI) where adjuvant treatment will not be given and it could be argued that in these cases POLE testing is not necessary. Applying these criteria, Talhouk et al. 9 found that POLE testing could be avoided in 55% of biopsy specimens and 38% of hysterectomy specimens. POLE testing should be performed on all MMRd and p53abn endometrial carcinomas in order not to miss a double‐classifier that would fall into the POLE mut group. A challenge is to identify features that are of prognostic and predictive significance in the most common NSMP group. This comprises a heterogeneous group with good prognosis low‐grade endometrioid carcinomas, high‐grade endometrioid carcinomas, and aggressive tumor types, such as clear cell carcinoma, mesonephric‐like adenocarcinoma, and gastric‐type adenocarcinoma. In this group, hormone receptor positivity may be of prognostic and therapeutic value since the ER and progesterone receptor (PR) are usually positive in low‐grade endometrioid carcinomas while the aggressive tumor types just listed are typically negative. Tumor grading is also of most prognostic value in the NSMP group. 25 It is also worth making the point that molecular classification will always be complementary to traditional pathological parameters since features such as tumor grade, depth of myometrial invasion, LVSI, and cervical and nodal involvement, which are prognostically and therapeutically significant, can only be identified on morphological examination.

WGM is responsible for the design and writing of the paper, and agrees to be accountable for all aspects of the published paper.

The STK11 adnexal tumor is a rare, recently described neoplasm that may be associated with Peutz–Jeghers syndrome (PJS). In the original report of this neoplasm, 47% of patients were known to have PJS with STK11 germline mutations. 104 Tumors have occurred in patients with a wide age range (16–74 years) and predominately originate in the para‐adnexal soft tissues, sometimes with secondary involvement of the fallopian tube and ovary. 104 , 105 These are aggressive tumors with frequent metastases and recurrences. STK11 adnexal tumors are morphologically heterogeneous with a wide range of different architectural patterns and cytological features. While their immunohistochemical profile is non‐specific, they typically have a “polyphenotypic” immunophenotype, often with positivity for cytokeratins, hormone receptors, mesothelial, and sex‐cord markers. Due to their location and heterogeneous morphology and immunoprofile, STK11 adnexal tumors have a broad differential diagnosis, including various Müllerian carcinomas (especially endometrioid carcinoma), mesothelioma, female adnexal tumor of Wolffian origin (FATWO), and sex cord–stromal tumors. Currently, the diagnosis of an STK11 adnexal tumor requires molecular confirmation of STK11 inactivation/alterations. The reporting pathologist must have a high index of suspicion to think of the diagnosis and instigate molecular testing. It is likely that many tumors previously reported as malignant FATWOs represent STK11 adnexal tumors. When making a diagnosis of STK11 adnexal tumor, the pathologist should mention the possibility of PJS on the pathology report if the patient is not already known to have this syndrome.

Until relatively recently, almost all uterine sarcomas were considered to represent leiomyosarcomas, low‐grade endometrial stromal sarcomas, undifferentiated sarcomas, or rare “heterologous” sarcomas, such as rhabdomyosarcoma. However, the last decade has witnessed the description of several “new” uterine sarcoma types, such as high‐grade endometrial stromal sarcomas associated with YWHAE‐NUTM2A/B or BCOR abnormalities, undifferentiated sarcomas associated with SMARCA4 mutation, and sarcomas associated with neurotrophic tropomyosin receptor kinase ( NTRK ) rearrangements (these predominantly have a cervical location) and KAT6A/B:: KANSL1 fusions. 49 , 50 , 51 , 52 , 53 , 54 , 55 Predominantly these neoplasms were discovered using molecular techniques, such as NGS, which have revealed novel diagnostic molecular events. Various other molecular abnormalities have also been reported in uterine sarcomas and with the increasing availability of these molecular techniques it is inevitable that additional “new” entities will be reported in the near future. This will result in diminution of the category of undifferentiated uterine sarcoma. Although many of these entities can be suspected on morphological and immunohistochemical examination, a definitive diagnosis of most of these neoplasms requires molecular confirmation. Since these are rare neoplasms and the testing infrastructure is not available in most pathology laboratories (even those with NGS panels), diagnosis will be facilitated by referral to centers that can undertake the necessary testing and to specialist pathologists. The last few years has also witnessed the publication of several studies that help to predict the behavior of uncommon uterine mesenchymal lesions, such as perivascular epithelioid cell tumor (PEComa), inflammatory myofibroblastic tumor (IMT), and uterine tumor resembling ovarian sex cord tumors (UTROSCTs). 56 , 57 , 58 , 59 , 60

It is not rare for a patient to have an endometrioid carcinoma in the endometrium and one, or occasionally both, ovaries. Traditionally, a combination of pathological parameters was used by pathologists to distinguish between synchronous independent primaries and metastasis usually from the endometrium to the ovary. It was long considered that, especially when both the endometrial and ovarian neoplasms are low‐grade, most of these represent dual independent primaries and the prognosis has been assumed to be good, although there are few studies with long‐term follow‐ups. Recent studies have demonstrated that most, but not all, endometrioid neoplasms involving both the endometrium and ovary are clonal, likely representing metastasis from the endometrium to the ovary. 26 , 27 , 28 Thus, there is a dilemma in that, although molecularly these are clonal neoplasms and most represent stage IIIA endometrial carcinomas, the prognosis is thought to be good. There is potential for overtreatment with the unnecessary administration of adjuvant therapy. In WHO 2020 and FIGO 2023, it is recommended that management (generally conservative management without adjuvant therapy) should be as for synchronous neoplasms when the following four criteria are met: (1) both tumors are low‐grade; (2) less than 50% myometrial invasion; (3) no involvement of any other site; and (4) absence of substantial LVSI at any location. In FIGO 2023, such neoplasms are staged as IA3. However, even here there are some inconsistencies between FIGO and WHO, in that bilateral ovarian involvement is not included in the criteria for synchronous neoplasms in FIGO 2023 but is allowable in the 2020 WHO classification.

The 2020 WHO Classification of Female Genital Tract Tumors (5th edition) was published online and in the traditional “Blue Book” in 2020. 1 Currently, this Classification is being updated and the sixth edition is expected to be published in 2026. This review covers significant recent developments and major changes in the classification of gynecological cancers, some of which emanate from the 2020 WHO Classification and a few others that have followed. Most of the topics discussed herein cannot be covered in detail and the reader is referred to the key references provided. New technologies, such as single‐cell technologies, liquid biopsies, ascitic fluid profiling, molecular cytopathology, and artificial intelligence, are likely to play an increasing role but these are not discussed in this review.

The author has no conflicts of interest.

LVSI has long been regarded as an important prognostic parameter in endometrial carcinoma and has gained increasing interest in recent years due to an expanding body of evidence of its independent prognostic value, especially when the presence of LVSI is quantified. A recent review has covered many aspects of LVSI in endometrial carcinoma. 29 A key strength of LVSI as a prognostic parameter is that it can be detected on routine microscopic examination, without ancillary tests, and thus can be used in low‐resource settings. A weakness, however, is the lack of uniformly applied criteria for the assessment and quantification of LVSI, resulting in inter‐observer variation in diagnosis. 29 , 30 These difficulties are compounded by artifacts and other morphological features that may mimic LVSI (commonly referred to as pseudo‐LVSI). Despite these issues, multiple studies have shown that LVSI, especially substantial or extensive LVSI, is strongly associated with lymph node metastasis and is an independent risk factor for nodal recurrence and distant metastasis. 29 , 31 , 32 , 33 Consequently, the presence of substantial LVSI has become an important consideration in formulating adjuvant treatment recommendations in patients with endometrial carcinoma. This has been incorporated into management guidelines, such as ESGO/ESTRO/ESP guidelines 23 and into the recent FIGO 2023 staging system. 24 Mimics of LVSI include tumor “smearing” and retraction artifacts, which are often secondary to poor fixation. Tumor displacement into vessels may also occur secondary to the use of an intrauterine manipulator during surgery; 34 these devices are transvaginally inserted into the uterine cavity and allow the surgeon to manipulate the uterus to improve access in the pelvis and identify anatomic structures. However, with manipulator use, tumor cells can be displaced into small and large vascular channels, slit‐like artefactual spaces within the myometrium (which are caused by the manipulator), lumina of the fallopian tubes or beyond. Clues to recognizing this form of pseudo‐LVSI are that the degree of vascular involvement is often greater than would be expected based on the grade and stage of the tumor (for example, in a low‐grade endometrioid carcinoma with minimal myometrial invasion, substantial LVSI would not be expected) and that the tumor emboli often preferentially involve large caliber blood vessels. The microcystic elongated and fragmented (MELF) pattern of myometrial invasion is associated with LVSI but can also mimic true LVSI. 35 One major problem is that there are no standardized criteria for substantial LVSI resulting in obvious problems. FIGO 2023 uses involvement of five or more lymphovascular spaces to define substantial LVSI, as does the 2020 WHO Classification 1 and the ESGO/ESTRO/ESP management guidelines. 23 The National Comprehensive Cancer Network (NCCN) guidelines use four or more spaces in at least one H&E slide 36 and three or more spaces is used in the 2022 International Collaboration on Cancer Reporting, 37 the 2019 ISGyP Endometrial Cancer Project recommendations, 38 and the 2023 CAP cancer reporting protocol. 39 In most of these recommendations, it is not clarified whether the extent of LVSI is based on the maximum involvement in a single tissue section or on the cumulative extent across all tissue sections. These factors result in difficulties in comparability between practices and regions. For example, if one institution has a very rigorous approach and a high threshold for diagnosis of substantial LVSI, a stage drift compared to other centers will develop. This will result in differing outcomes between centers, stage by stage, not due to real differences in patient outcome, but secondary to systematic differences in stage assignment (the so‐called “stage migration effect”). An additional complicating factor is that a recent large study showed that focal and substantial LVSI in endometrial carcinomas were both associated with increased risk of disease progression but were not prognostically distinct suggesting that focal versus no LVSI have different prognostic outcomes and should not be combined into one category. 40