W Glenn McCluggage

Editorial: Infiltrative pattern of invasion is independently associated with shorter survival and desmoplastic stroma markers FAP and THBS2 in mucinous ovarian carcinoma

Editorial on: Role of gene sequencing in classifying struma ovarii: BRAF P.G469A mutation and TERT promoter alterations favour malignant struma ovarii

FIGO 2023 endometrial cancer staging system: recommendations for the UK

FIGO 2023 endometrial cancer staging: too much, too soon?

An updated International Federation of Gynecology and Obstetrics (FIGO) staging system for endometrial carcinoma was introduced in June 2023. The new system represents a significant departure from traditional endometrial and other gynecological carcinoma staging systems which are agnostic of parameters such as tumor type, tumor grade, lymphovascular space invasion, and molecular alterations. The updated system, which incorporates all of these 'non-anatomical' parameters, is an attempt to make staging more personalized and relevant to patient prognostication and management, and to align with the European Society of Gynaecological Oncology/European Society for Radiotherapy and Oncology/European Society of Pathology (ESGO/ESTRO/ESP) risk stratification. Herein, we present a critical review of the new staging system and discuss its advantages and disadvantages. The authors propose that the new FIGO staging system should be first appraised at a multi-institutional and global level with the input of all relevant societies (gynecology, pathology, gynecologic oncology, medical oncology, radiation oncology) to understand the impact, scope, and supporting evidence of the proposed changes. Such a process is fundamental to produce a robust system that pathologists and treating clinicians can adopt.

Clinical Behavior and Molecular Landscape of Stage I p53-Abnormal Low-Grade Endometrioid Endometrial Carcinomas

Abstract Purpose: The clinical significance of the p53-abnormal (p53abn) molecular subtype in stage I low-grade endometrioid endometrial carcinoma (EEC) is debated. We aimed to review pathologic and molecular characteristics, and outcomes of stage I low-grade p53abn EEC in a large international cohort. Experimental Design: Previously diagnosed stage I p53abn EC (POLE–wild-type, mismatch repair–proficient) low-grade EEC from Canadian retrospective cohorts and PORTEC-1&2 trials were included. Pathology review was performed by six expert gynecologic pathologists blinded to p53 status. IHC profiling, next-generation sequencing, and shallow whole-genome sequencing was performed. Kaplan–Meier method was used for survival analysis. Results: We identified 55 stage I p53abn low-grade EEC among 3,387 cases (2.5%). On pathology review, 17 cases (31%) were not diagnosed as low-grade EEC by any pathologists, whereas 26 cases (47%) were diagnosed as low-grade EEC by at least three pathologists. The IHC and molecular profile of the latter cases were consistent with low-grade EEC morphology (ER/PR positivity, patchy p16 expression, PIK3CA and PTEN mutations) but they also showed features of p53abn EC (TP53 mutations, many copy-number alterations). These cases had a clinically relevant risk of disease recurrence (5-year recurrence-free survival 77%), with pelvic and/or distant recurrences observed in 12% of the patients. Conclusions: A subset of p53abn EC is morphologically low-grade EEC and exhibit genomic instability. Even for stage I disease, p53abn low-grade EEC are at substantial risk of disease recurrence. These findings highlight the clinical relevance of universal p53-testing, even in low-grade EEC, to identify women at increased risk of recurrence.

Correlation between P53 immunohistochemical staining and TP53 molecular testing in endometrial carcinomas: a detailed assessment of discrepant cases with implications for patient management

Aims The 2013 Cancer Genome Atlas (TCGA) study identified four molecular types of endometrial carcinoma (EC) that are prognostic and predictive of therapy response. The p53 abnormal (p53abn) group of tumours is associated with aggressive clinical behaviour, chemoresponsiveness and generally high‐grade histology. p53abn tumours may be identified by p53 immunohistochemical staining (a surrogate marker) or molecular testing. In this study, we evaluated the concordance between p53 immunohistochemistry and TP53 molecular testing in a consecutive cohort of ECs from a population‐based setting. Our aim was to investigate the rate of concordance and reasons for discordance between the immunohistochemistry and molecular testing and to provide recommendations for pathologists and clinicians dealing with these discordant cases. Methods and results A total of 386 ECs were included where all biopsy specimens underwent molecular testing using a next‐generation sequencing (NGS) panel (including POLE and TP53 genes and MSI testing) and immunohistochemistry for oestrogen receptor (ER), p53 and mismatch repair (MMR) proteins. Concordance between p53 immunohistochemistry and TP53 NGS was initially 88.6% (discordance of 11.4%) following review of the pathology and molecular reports; most of the discordant cases comprised carcinomas with wild‐type p53 immunohistochemistry but TP53 mutations identified on NGS. The discordance reduced to 6.5% after review of the p53 stained slides, which revealed subclonal mutation‐type staining in some tumours, and to 5% after excluding POLE mutated and mismatch repair deficient carcinomas. However, there remained a small cohort of 19 POLE wild‐type/MMR proficient carcinomas (8 low‐grade endometrioid, 9 high‐grade endometrioid, 2 carcinosarcomas), with wild‐type p53 staining but with TP53 mutations on NGS. Altogether, there were 12 POLE wild‐type/MMR proficient low‐grade endometrioid carcinomas with TP53 mutations on NGS; all were stage I (11 IA, 1 IB). Conclusions Our study demonstrated a good overall concordance between p53 immunohistochemical staining and TP53 molecular results. The concordance can be increased by reviewing the p53 stained slides in discrepant cases but there remains a small cohort of cases, mostly low‐grade endometrioid carcinomas ( POLE wild‐type/MMR proficient), where TP53 mutations are present on NGS but p53 immunohistochemistry is wild‐type. Such cases present a dilemma for the pathologist (which TCGA group should they be placed into) and the clinician (should adjuvant therapy be instigated based on the presence of a TP53 mutation alone with no other adverse features). For now, we advise classifying such cases as p53abn but not to administer adjuvant therapy based on the presence of a TP53 mutation alone without other adverse pathological factors. The significance of TP53 mutations in such cases should be determined by larger studies with long‐term follow‐up.

Initiation of molecular testing of endometrial carcinomas in a population‐based setting: practical considerations and pitfalls

AimsSince the publication of The Cancer Genome Atlas (TCGA) molecular Classification of endometrial carcinomas in 2013, multiple studies have demonstrated the prognostic and therapeutic importance of this. However, there is great variability on whether and how this is undertaken in different institutions, and this is often dependent on resources and availability of molecular testing. Points of controversy include whether molecular classification is needed on all endometrial carcinomas and whether pure molecular testing is undertaken or a surrogate such as the ProMisE (Proactive Molecular Risk Classifier for Endometrial Cancer) Classifier. Herein we report our experience instigating molecular classification of endometrial carcinomas in Northern Ireland.Methods and ResultsFrom 1st March 2023, all endometrial carcinomas diagnosed on biopsy in the four pathology laboratories in Northern Ireland were referred to the central molecular pathology laboratory for genomic analysis using a custom next‐generation sequencing (NGS) panel; the NGS panel included the entire coding regions of polymerase epsilon (POLE) and TP53 genes, as well as microsatellite instability (MSI) analysis. All cases also underwent immunohistochemical staining with oestrogen receptor (ER), p53, and the mismatch repair (MMR) proteins MLH1, PMS2, MSH2, and MSH6. The molecular results were available by the time of surgery (if a hysterectomy was performed) allowing integration into the final pathology report where a TCGA molecular type was assigned. Two hundred and sixty‐seven endometrial carcinomas underwent molecular testing; in five cases, there was insufficient material for testing, leaving 262 cases. The TCGA groups were POLEmut (19; 7.3%), MMRd (63; 24%), p53abn (62; 23.7%), and no specific molecular profile (NSMP) 118 (45%). Seventeen tumours (6.5%) were “multiple‐classifiers”: five POLEmut‐p53abn, two POLEmut‐MMRd, one POLE‐MMRd‐p53abn (all included in the POLEmut TCGA group), and nine MMRd‐p53abn (included in the MMRd group).ConclusionThis represents one of the first population‐based studies investigating the prevalence of the different TCGA molecular groups of endometrial carcinomas in an unselected population. Performing molecular testing on biopsies enables management to be tailored to the molecular group and allows integration of the TCGA group into the report of the final resection specimen. We hope our experience will facilitate other laboratories in undertaking TCGA molecular classification.

Practical guidance for assessing and reporting lymphovascular space invasion (LVSI) in endometrial carcinoma

Lymphovascular space invasion (LVSI) is an important prognostic parameter in endometrial carcinoma (EC) 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 key strength of LVSI as a prognostic factor 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 assessment and quantification of LVSI, resulting in interobserver variation in diagnosis. This is confounded by artefacts and other morphological features that may mimic LVSI (commonly referred to as pseudo‐LVSI). Despite these issues, multiple studies have shown that LVSI is strongly associated with lymph node (LN) metastasis and is an independent risk factor for LN recurrence and distant metastasis. Consequently, the presence of substantial/extensive LVSI has become an important consideration in formulating adjuvant treatment recommendations in patients with EC, and this has been incorporated in the recent International Federation of Gynecology and Obstetrics (FIGO) 2023 staging system. Herein, we review the current literature on LVSI in EC and discuss its role as a prognostic marker, the reproducibility of LVSI assessment and distinction between LVSI and its mimics. We provide illustrations of key diagnostic features and discuss the two‐tiered (none/focal versus substantial) system of LVSI classification. This work is intended to provide guidance to practising pathologists and unify the approach towards LVSI assessment in EC.

SOX17 expression in mesonephric‐like adenocarcinomas and mesonephric remnants/hyperplasia of the female genital tract: Expanding its utility as a Müllerian biomarker

AimsRecently, SOX17 has emerged as a promising biomarker for non‐mucinous Müllerian (ovarian and endometrial) carcinomas, demonstrating increased specificity in comparison to PAX8 while maintaining similar sensitivity. However, expression of SOX17 in mesonephric‐like adenocarcinoma (MLA), a carcinoma of the female genital tract with uncertain, but probably Müllerian histogenesis, remains unexplored. This study aims to address this gap.Methods and resultsSOX17 immunohistochemistry was performed on whole tissue sections from 68 MLAs originating from the endometrium or ovary and seven cervical mesonephric carcinomas, as well as six mesonephric remnants/hyperplasias. Using a four‐tiered scoring system based on distribution and intensity of staining, 68% of MLA displayed a negative/low (< 10%) SOX17 expression pattern, which contrasts with the high expression observed in most Müllerian carcinomas. However, 22% of MLA demonstrated high SOX17 expression, similar to other endometrial and ovarian carcinomas. Similarly, five of seven (72%) mesonephric carcinomas of the cervix were SOX17‐negative, but two cases (28%) were positive. All mesonephric remnants/hyperplasias were SOX17 negative.ConclusionsThe majority of MLA are negative or exhibit low SOX17 expression, in contrast to the diffuse and strong expression commonly seen in other types of Müllerian carcinoma. However, a subset of MLAs demonstrate high SOX17 expression. Therefore, absence of SOX17 staining is supportive for MLA when the differential includes another non‐mucinous Müllerian carcinoma. SOX17 may also be useful for differentiating mesonephric remnants/hyperplasias from Müllerian malignancies and benign Müllerian glandular lesions.

Clinical utility of pathology data: endometrial and tubo-ovarian carcinomas

Cancer resection specimens are usually reported using standardised proformas that consist of a list of elements, which include core (required) and non-core (recommended) items. Although all elements are generally included in the reports, the clinical importance of a particular parameter often depends on a variety of factors, including the clinical setting, local management guidelines and other pathological parameters. In this review, we briefly outline how histopathology data are used to guide management of patients with endometrial and tubo-ovarian cancers, the most common gynaecological malignancies, and provide advice as to which data elements are important in particular scenarios.

Endometrial neuroendocrine carcinoma and undifferentiated carcinoma are distinct entities with overlap in neuroendocrine marker expression

AimsDedifferentiated endometrial carcinomas (DDECs)/undifferentiated endometrial carcinomas (UDECs) frequently harbour genomic activation of switch/sucrose non‐fermentable (SWI/SNF)‐complex proteins, and can show histological overlap with neuroendocrine carcinoma (NEC). The aim of this study was to compare the extent of the expression of neuroendocrine markers, SWI/SNF proteins and mismatch repair (MMR) proteins in DDEC/UDEC and NEC.Methods and resultsThe extent of expression of synaptophysin, chromogranin, CD56, ARID1A, ARID1B, SMARCA4, SMARCB1 and MMR proteins was evaluated by immunohistochemistry on 44 SWI/SNF‐deficient DDECs/UDECs and 15 NECs. Thirty‐three of 44 (75%) DDECs/UDECs showed expression of at least one neuroendocrine marker, with 18 of 44 (41%) expressing two or more neuroendocrine markers, whereas all 15 NECs showed expression of at least one neuroendocrine marker, with 14 of 15 (93%) expressing two or more neuroendocrine markers. Neuroendocrine marker expression in DDECs/UDECs was typically focal when present, with average extents of 17%, 4% and 8% for synaptophysin, chromogranin and CD56 in the positive cases, respectively, in contrast to 73%, 40% and 62% in the positive NEC cases, respectively. All 15 NECs showed intact expression of SWI/SNF‐complex proteins, except for one that showed isolated loss of ARID1A. Thirty‐eight of 44 DDECs/UDECs were MMR‐abnormal (34 with loss of MLH1 and PMS2, and four with loss of PMS2 alone), whereas all NECs retained MMR protein expression.ConclusionsOur study demonstrates frequent but typically focal neuroendocrine marker expression in SWI/SNF‐deficient DDECs/UDECs, whereas NECs typically express two or more neuroendocrine markers, with diffuse expression of at least one marker. ARID1B, SMARCA4 and SMARCB1 immunohistochemistry can be used to aid in the differentiation between DDEC/UDEC and NEC.

NTRK and other recently described kinase fusion positive uterine sarcomas: A review of a group of rare neoplasms

AbstractThe landscape of uterine sarcomas has greatly expanded in recent years to include neoplasms with recurrent gene fusions, such as BCOR and YWHAE translocated high‐grade endometrial stromal sarcomas. Sophisticated molecular techniques have also resulted in the description of “new” entities associated with recurrent kinase fusions involving NTRK and RET as well as COL1A1‐PDGFB rearranged uterine sarcomas. These rare neoplasms will be discussed in this review, highlighting that some of the underlying molecular events are clinically actionable and potentially susceptible to targeted therapy. While relatively few of these neoplasms have been described to date, likely being previously lumped under the spectrum of undifferentiated uterine sarcoma, the number of cases will expand in the future given their recognition and the increasing availability of molecular testing. These neoplasms have overlapping morphology (often with a “fibrosarcoma‐like” appearance) and immunohistochemical features, and are characterized by variable clinical outcomes. Although immunohistochemistry may assist in some cases, a definitive subclassification requires confirmatory molecular studies. As these molecular assays may not be routinely available in most laboratories, referral to reference centers may be needed. In order to assist the pathologist, we suggest a diagnostic algorithm for routine practice when dealing with a malignant or potentially malignant uterine spindle cell neoplasm.

Endometriosis‐related pathology: a discussion of selected uncommon benign, premalignant and malignant lesions

Endometriosis is an extremely common condition and, in most cases, establishing a histological diagnosis is straightforward, although a variety of benign alterations may result in problems with interpretation. In this review, I discuss selected uncommon variants of endometriosis or benign alterations that may result in diagnostic problems. The topics covered include the contentious issue of so‐called atypical endometriosis, stromal endometriosis, polypoid endometriosis, and the association of endometriosis with florid mesothelial hyperplasia. The propensity of endometriosis to undergo neoplastic transformation (especially to endometrioid and clear cell carcinoma) is well known. Selected issues relating to the various neoplasms that can arise in endometriosis are discussed, with a particular concentration on unusual variants of endometrioid carcinoma that result in a disproportionately high number of issues in referral practice. The propensity of ovarian endometrioid carcinomas to show an unexpected (‘aberrant’) immunophenotype with positive staining with ‘intestinal’ markers and negative staining with Mullerian markers is also discussed. Uncommon tumour types that may arise in endometriosis, namely seromucinous neoplasms, mesonephric‐like carcinomas, and somatically derived yolk sac tumours, are also covered.

Tubo‐ovarian high‐grade serous carcinomas commonly express CA19.9

β‐catenin signatures in the fallopian tube: an emerging concept

STK11 (LKB1) immunohistochemistry is a sensitive and specific marker for STK11 adnexal tumours

AimsSTK11 adnexal tumour is a rare, recently described malignant neoplasm that is associated with Peutz–Jeghers syndrome. [Correction added on 3 October 2024, after first online publication: ‘ST11’ in preceding sentence has been corrected to ‘STK11’ in this version.] It predominantly originates from the para‐adnexal soft tissues and often shows secondary involvement of the fallopian tube and ovary. STK11 adnexal tumours have a broad differential diagnosis due to their variable morphology and non‐specific immunoprofile, and diagnostic confirmation currently requires sequencing to identify an STK11 mutation. We investigate the diagnostic utility of STK11 (LKB1) immunohistochemistry (IHC) in a cohort of STK11 adnexal tumours and morphological mimics.Methods and resultsIHC for STK11 was performed on 122 tumours, including 17 STK11 adnexal tumours and 105 morphological mimics (10 female adnexal tumours of Wolffian origin, 22 adult granulosa cell tumours, 10 juvenile granulosa cell tumours, four Sertoli–Leydig cell tumours, two Leydig cell tumours, one Sertoli cell tumour, one steroid cell tumour, four extra‐ovarian sex cord‐stromal tumours, 16 ovarian endometrioid carcinomas, eight tubo‐ovarian high‐grade serous carcinomas, five ovarian mesonephric‐like adenocarcinomas, 14 ovarian carcinosarcomas, five peritoneal malignant mesotheliomas, two pelvic plexiform leiomyomata and one ovarian solid pseudopapillary tumour). All STK11 adnexal tumours showed complete loss of cytoplasmic staining for STK11. All other tumour types showed retained cytoplasmic staining, except for one endometrioid carcinoma with mucinous differentiation which showed complete loss of STK11 expression and a high‐grade serous carcinoma with subclonal loss.ConclusionsSTK11 is a highly sensitive and specific immunohistochemical marker for distinguishing STK11 adnexal tumour from its histological mimics, and can obviate the need for confirmatory molecular studies in the appropriate morphological context.

Gastric‐type glandular lesions of the female genital tract excluding the cervix: emerging pathological entities

In the last two decades or so, a spectrum of benign, premalignant and malignant cervical glandular lesions exhibiting gastric differentiation has been described, with gastric‐type adenocarcinoma representing the most common human papillomavirus (HPV)‐independent cervical adenocarcinoma. More recently, limited literature has reported a variety of gastric‐type glandular lesions at other sites within the female genital tract and, as in the cervix (the most common site for these lesions), a spectrum of benign, premalignant and malignant lesions has been proposed. We provide an update and review of the emerging spectrum of gastric‐type glandular lesions at female genital tract sites other than the cervix. In the endometrium, putative gastric‐type glandular lesions include mucinous metaplasia of gastric‐type, atypical mucinous proliferation of gastric‐type and gastric‐type adenocarcinoma. Similarly in the vagina, gastric‐type adenosis, atypical adenosis and adenocarcinoma have been described. There have also been occasional reports of gastric‐type lesions involving the ovary and fallopian tube. We provide guidance on how to recognise gastric‐type lesions morphologically and immunophenotypically and stress that sometimes these lesions occur at more than one site within the female genital tract (synchronous/multifocal gastric‐type lesions of the female genital tract), sometimes in association with Peutz–Jeghers syndrome.

Ovarian seromucinous cystadenomas and adenofibromas: first report of a case series

AimsTo report a series of benign ovarian seromucinous neoplasms, an uncommon and hitherto poorly described category of tumours included in the current 2014 World Health Organisation classification of tumours of the female reproductive organs.Methods and resultsWe report the clinicopathological features of a series of 22 benign ovarian seromucinous neoplasms (cystadenomas and adenofibromas or admixtures). The neoplasms occurred in patients aged 32–83 years (mean = 62, median = 65.5) and involved the left ovary (n = 14), the right ovary (n = 6) or both ovaries (n = 2). There was a common association with endometrioid elements (endometrioid differentiation within the cystadenoma/adenofibroma and/or endometriosis) and other endometriosis‐associated neoplasms.ConclusionsWe speculate that some of these represent benign ovarian endometrioid neoplasms with foci of mucinous and/or serous differentiation, while others represent true mixed neoplasms.

SWI/SNF protein and claudin‐4 expression in anaplastic carcinomas arising in mucinous tumours of the ovary and retroperitoneum

AimsAnaplastic carcinoma arising in a mucinous tumour of the ovary and rarely in the retroperitoneum is an uncommon neoplasm with three morphological patterns; rhabdoid, sarcomatoid and pleomorphic. We investigated expression of switch/sucrose non‐fermentable (SWI/SNF) chromatin remodelling complex components and claudin‐4 expression.Methods and resultsTwenty‐two ovarian and three retroperitoneal mucinous tumours were investigated using antibodies against SMARCB1, SMARCA4, SMARCA2, ARID1A and claudin‐4. Loss of nuclear staining for any SWI/SNF protein was observed in the anaplastic component of nine of 25 (36%), with retained expression within the mucinous component of all tumours. Five (56%) showed loss of more than one protein, with dual loss of SMARCA4 and SMARCA2 in two, loss of SMARCA2 and ARID1A in two and loss of SMARCB1 and SMARCA2 in one. Retained expression of claudin‐4 was seen in 39% of the anaplastic carcinomas and within the mucinous component of all tumours. Rhabdoid morphology was associated with poor prognosis [stages III or IV disease (six of six, 100% versus four of 14, 29%; P = 0.0108] and death from disease (three of four, 75% versus one of 13, 8%; P = 0.0223). Although loss of a SWI/SNF protein was not significantly associated with death from disease (three of five, 60% versus one of 12, 8%; P = 0.0525), it showed a trend in correlation with poor prognosis and was often noted in tumours with rhabdoid morphology within this small cohort.ConclusionsOur report adds to the growing list of female genital tract malignancies with loss of SWI/SNF proteins, underlining their broad differential diagnosis and the importance of careful, context‐dependent interpretation of SWI/SNF protein loss.

High-risk human papillomavirus (HPV) detection in formalin-fixed paraffin-embedded cervical tissues: performances of Aptima HPV assay and Beckton Dickinson (BD) Onclarity assay

Aim There are many scenarios where high-risk human papillomavirus (HPV) detection in formalin-fixed paraffin-embedded (FFPE) specimens is important. However, there is no Food and Drug Administration (FDA)-approved and clinically validated technique for detecting high-risk HPV in FFPE tissues. In this study, we evaluated two commercially available HPV assays which are FDA-approved for use on cytology specimens, the Aptima HPV assay and the Beckton Dickinson (BD) Onclarity assay, to detect high-risk HPV in FFPE tissues of cervical high-grade squamous intraepithelial lesion (HSIL) and squamous cell carcinoma (SCC). Methods A total of 189 cases (46 SCC, 107 HSIL and 36 benign/normal) were tested for high-risk HPV with the Aptima HPV assay and a subset of cases (n=97) with the BD Onclarity assay. Results The sensitivities of the Aptima and BD Onclarity HPV assays were 99.4% (95% CI 96.46% to 99.98%) and 75.9% (95% CI 65.27% to 84.62%), respectively; the specificity and positive predictive value (PPV) of the two assays were 100%. Negative predictive values of the Aptima and BD Onclarity HPV assays were 97.3% (95% CI 83.61% to 99.61%) and 67.7% (95% CI 58.91% to 75.47%), respectively. The kappa value (0.96) for comparison of the distribution of high-risk HPV types between the two assays was high. HPV 16 was the most common high-risk HPV type for HSIL and SCC cases. However, SCC cases had higher percentages of HPV 16 and HPV 18/45 and lower percentages of other high-risk HPV types compared with HSIL cases. Conclusion Both assays are reliable methods for high-risk HPV detection and genotype determination in FFPE specimens, with high PPV and specificity. The Aptima HPV assay has the advantage of higher sensitivity. As far as we are aware, this is the first study comparing the Aptima HPV assay and the BD Onclarity assay in FFPE tissues. Our study results should be tested and confirmed in larger cohorts.

Ovarian microcystic stromal tumour: from morphological observations to syndromic associations

Microcystic stromal tumour (MST) is a rare, usually benign, ovarian neoplasm characterized morphologically in its classic form by a distinctive triad of features comprising microcysts, solid cellular regions and fibrous stroma. Variant morphology also occurs, including the presence of nests, tubules, cords and signet ring cells. Immunohistochemically, this neoplasm is characterized by diffuse nuclear expression of β‐catenin, cyclin D1, Wilms' tumour 1 (WT1) and steroidogenic factor 1 (SF1), as well as diffuse staining with forkhead box ligand 2 (FoxL2) and CD10. Inhibin and calretinin are typically negative. At the genomic level, these neoplasms harbour mutually exclusive mutations in CTNNB1 or APC genes, with the former being significantly more common. This molecular characteristic raises possible links to other rare ovarian lesions, including solid pseudopapillary tumour, signet‐ring stromal tumour and Sertoli cell tumour. Rarely, MST is an extracolonic manifestation of familial adenomatous polyposis (FAP) and serves as a sentinel event that could trigger the identification of the syndrome. Herein, we review the published literature on ovarian MST and provide practical advice for pathologists reporting these rare neoplasms.

A Subset of SMARCB1 (INI‐1)‐deficient vulvar neoplasms express germ cell markers

AimsSMARCB1 (INI‐1)‐deficient vulvar neoplasms comprise a group of rare tumours that include epithelioid sarcoma (ES), myoepithelial carcinoma (MEC), the recently described myoepithelioma‐like tumour of the vulvar region (MELTVR), and sarcomas that are difficult to classify. It has been suggested that so‐called vulvar yolk sac tumours (YST) may represent morphologic variants of SMARCB1‐deficient tumours; thus, we investigated the immunoreactivity of germ cell markers in SMARCB1‐deficient vulvar neoplasms.Methods and resultsTen SMARCB1‐deficient vulvar neoplasms were stained with germ cell tumour markers (SALL4, glypican‐3, OCT3/4, and AFP) and re‐reviewed for morphologic features. The tumours occurred in adult females (median age 41 years) and included ES (n = 7), MELTVR (n = 2), and MEC (n = 1). All cases showed loss of SMARCB1 expression. Four cases (40%) were focally positive for SALL4 in areas with morphology of typical‐appearing ES. One of these cases also showed focal staining for OCT3/4. One ES showed a transition from typical‐appearing ES to YST‐like morphology, with diffuse expression of SALL4 and glypican‐3, and focal expression of AFP, in these latter areas. All other tested cases were negative for AFP.ConclusionOur study reveals that SALL4, glypican‐3, and OCT3/4 are positive in a subset of SMARCB1‐deficient vulvar neoplasms, which may pose a diagnostic challenge and result in consideration of a germ cell tumour. We also highlight a case with transition from ES to YST‐like morphology, lending further support that YSTs of the vulva are somatically derived SMARCB1‐deficient neoplasms and do not represent true germ‐cell neoplasia.

Ovarian Sertoli–Leydig cell tumors with heterologous rhabdomyosarcoma: Clinicopathologic features and molecular analysis highlighting recurrent genetic alterations

Aims Ovarian Sertoli–Leydig cell tumor (SLCT) with heterologous rhabdomyosarcoma (RMS) is exceptionally rare. While the presence of heterologous elements in SLCT is highly predictive of an underlying DICER1 mutation, the molecular alterations in these tumors, including in SLCTs with heterologous RMS, remain largely unknown. In this study, we aimed to characterize the clinicopathologic features of these rare tumors, and in a subset of cases, we analyzed in detail their molecular changes to investigate potential recurrent and component‐specific genetic alterations. Methods and results We report clinicopathologic features of 11 ovarian SLCTs with heterologous RMS (positivity for desmin and myogenin); 10 were in keeping with embryonal and 1 with pleomorphic RMS. The patients showed a bimodal age distribution: seven patients (64%) were aged 33 years or younger (mean 20) and four patients (36%) were aged 52 years or older (mean 60). All tumors were unilateral. In addition to the RMS components, 8 of 11 cases (73%) contained other heterologous elements, including gastrointestinal‐type mucinous epithelium (5 cases) and immature cartilage (3 cases). Seven of 11 cases (64%) underwent next‐generation sequencing analysis. All tumors tested molecularly (7/7, 100%) harbored hotspot DICER1 mutations. Of these, six cases (86%) also carried a second nonsense or frameshift loss‐of‐function DICER1 mutation. One case had only a p.D1810Y hotspot mutation and consisted of high‐grade sarcoma with focal rhabdomyoblastic differentiation (focal expression of desmin and myogenin) in keeping with pleomorphic RMS; the pleomorphic sarcoma component also exhibited mutation‐type p53 expression. In addition to DICER1 mutations, TERT c.‐124C>T promoter (4 cases) or TP53 mutations (3 cases) were present in all cases and were mutually exclusive. Component‐specific analysis in two cases revealed shared common DICER1 hotspot mutations in both the SLCT and RMS components, supporting a clonal origin. In 1 case, a TERT promoter c.‐124C>T somatic mutation was present only in the RMS component. In the other case, the TERT promoter mutation was found in both components, while a BRAF p.V600E mutation was exclusive to the RMS component. Conclusion Our study demonstrates that the majority (86%) of SLCTs with heterologous RMS harbor double DICER1 mutations (a hotspot mutation and a nonsense or frameshift loss‐of‐function mutation), supporting the existing knowledge on DICER1 mutations associated with RMS heterologous elements, the presence of which should trigger genetic counselling. Our findings also suggest that molecular alterations other than DICER1 , namely, TERT promoter and TP53 mutations, may contribute to component‐specific oncogenic transformation.

SMARCA4 Loss Increases RNA Polymerase II Pausing and Elevates R-Loops to Inhibit BRCA1-Mediated Repair in Ovarian Cancer

Abstract Small cell carcinoma of the ovary, hypercalcemic type (SCCOHT) is a rare, aggressive cancer affecting young women driven by inactivating mutations in SMARCA4, a key SWI/SNF chromatin remodeling gene. To uncover its druggable vulnerabilities, we performed a compound screen and found that SCCOHT cells and tumors were sensitive to PARP inhibitors. Paradoxically, SCCOHT displayed BRCA-deficient traits despite retaining wild-type BRCA1 expression. Elevated R-loop in SCCOHT sequestered BRCA1, limiting its availability for DNA damage repair. Proximity-dependent biotin identification revealed that wild-type SMARCA4, but not its pathogenic variants, promoted RNA polymerase II (Pol II) elongation by mediating the assembly of the polymerase-associated factor 1 complex. Thus, SMARCA4 loss increased Pol II pausing, resulting in elevated R-loops and BRCA1 redistribution. The suppression of BRCA1 activity sensitized SMARCA4-deficient SCCOHT cells and tumors to PARP inhibitors, which was further enhanced by the addition of a CDK9 inhibitor targeting Pol II elongation. Cotargeting PARP/CDK9 also elicited synergistic effects against other undifferentiated ovarian cancer cells with SMARCA4 loss. These findings link SMARCA4 loss to perturbed Pol II elongation and compromised DNA repair by BRCA1, providing a therapeutic opportunity to target SCCOHT and other SWI/SNF-deficient ovarian cancers. Significance: Pol II stalling induced by SMARCA4 loss leads to R-loop accumulation that sequesters BRCA1 to transcription complexes, underlying the sensitivity of SMARCA4-deficient ovarian cancers to inhibitors targeting PARPs and Pol II elongation.

Teratoma‐associated and so‐called pure Wilms tumour of the ovary represent two separate tumour types with distinct molecular features

AimsOvarian Wilms tumour (WT)/nephroblastoma is an extremely rare neoplasm that has been reported to occur in pure form or as a component of a teratomatous neoplasm. We hypothesized that teratoma‐associated and pure ovarian WT may represent different tumour types with diverging molecular backgrounds. To test this hypothesis, we comprehensively characterized a series of five tumours originally diagnosed as ovarian WT.Methods and ResultsThe five cases comprised three teratoma‐associated (two mature and one immature) and two pure WTs. Two of the teratoma‐associated WTs consisted of small nodular arrangements of “glandular”/epithelial structures, while the third consisted of both an epithelial and a diffuse spindle cell/blastemal component. The pure WTs consisted of “glandular” structures, which were positive for sex cord markers (including inhibin and SF1) together with a rhabdomyosarcomatous component. The two pure WTs harboured DICER1 pathogenic variants (PVs), while the three associated with teratomas were DICER1 wildtype. Panel‐based DNA sequencing of four of the cases did not identify PVs in the other genes investigated. Analysis of the HA19/IGF2 imprinting region showed retention of imprinting in the pure WTs but loss of heterozygosity with hypomethylation of the ICR1 region in two of three teratoma‐associated WTs. Furthermore, copy number variation and clustering‐based whole‐genome DNA methylation analyses identified divergent molecular profiles for pure and teratoma‐associated WTs.ConclusionBased on the morphological features, immunophenotype, and molecular findings (DICER1 PVs, copy number, and DNA methylation profiles), we suggest that the two cases diagnosed as pure primary ovarian WT represent moderately to poorly differentiated Sertoli Leydig cell tumours (SLCTs), while the tumours arising in teratomas represent true WTs. It is possible that at least some prior cases reported as pure primary ovarian WT represent SLCTs.

Pan‐TRK immunohistochemistry in gynaecological mesenchymal tumours: diagnostic implications and pitfalls

AimsNTRK‐rearranged sarcomas of the female genital tract mainly occur in the uterus (more commonly cervix than corpus) and are characterized by a “fibrosarcoma‐like” morphology and NTRK gene rearrangements. These neoplasms may exhibit histological overlap with other entities and can present diagnostic difficulties without molecular confirmation. Pan‐TRK immunohistochemistry was developed to identify tumours harbouring NTRK rearrangements. The aim of this study was to characterize pan‐TRK immunohistochemical expression in a large cohort of gynaecological mesenchymal neoplasms and investigate the utility of pan‐TRK immunohistochemistry to distinguish NTRK‐rearranged sarcoma from its mimics.Methods and resultsA total of 473 gynaecological mesenchymal tumours (461 without known NTRK fusions and 12 NTRK‐rearranged sarcomas) were selected. Pan‐TRK immunohistochemistry (EPR17341, Abcam) was performed on whole tissue sections and tissue microarrays. Molecular interrogation of pan‐TRK positive tumours was performed by RNA sequencing or fluorescence in situ hybridization (FISH). Of the 12 NTRK‐rearranged sarcomas, 11 (92%) exhibited diffuse (≥70%) cytoplasmic pan‐TRK staining with moderate/marked intensity, while the other was negative. Eleven (2.4%) additional tumours also exhibited pan‐TRK immunohistochemical expression: three low‐grade endometrial stromal sarcomas, seven high‐grade endometrial stromal sarcomas, and an undifferentiated uterine sarcoma. Molecular confirmation of the absence of NTRK rearrangements was possible in nine of these tumours. Of these nine neoplasms, seven exhibited focal/multifocal (<70%) pan‐TRK cytoplasmic staining with weak/moderate intensity.ConclusionEven though pan‐TRK immunohistochemical expression is not entirely sensitive or specific for NTRK‐rearranged sarcomas, these neoplasms tend to exhibit diffuse staining of moderate/strong intensity, unlike its mimics. Pan‐TRK should be performed in monomorphic uterine (corpus and cervix) spindle cell neoplasms that are negative for smooth muscle markers and hormone receptors and positive for CD34 and/ or S100. Ultimately, the diagnosis requires molecular confirmation.