Dedifferentiated and Undifferentiated Ovarian Carcinoma: An Aggressive and Molecularly Distinct Ovarian Tumor Characterized by Frequent SWI/SNF Complex Inactivation.

Dedifferentiated and undifferentiated ovarian carcinomas (DDOC/UDOC) are rare neoplasms defined by the presence of an undifferentiated carcinoma. In this study, we detailed the clinical, pathological, immunohistochemical, and molecular features of a series of DDOC/UDOC. We collected a multi-institutional cohort of 23 DDOC/UDOC and performed immunohistochemistry for core switch/sucrose nonfermentable (SWI/SNF) complex proteins (ARID1A, ARID1B, SMARCA4, and SMARCB1), mismatch repair (MMR) proteins, and p53. Array-based genome-wide DNA methylation and copy number variation analyses were performed on a subset of cases with comparison made to a previously reported cohort of undifferentiated endometrial carcinoma (UDEC), small cell carcinoma of the ovary, hypercalcemic type (SCCOHT), and tubo-ovarian high-grade serous carcinoma (HGSC). The age of all 23 patients with DDOC/UDOC ranged between 22 and 71 years (with an average age of 50 years), and a majority of them presented with extraovarian disease (16/23). Clinical follow-up was available for 19 patients. Except for 2 patients, the remaining 17 patients died from disease, with rapid disease progression resulting in mortality within a year in stage II-IV settings (median disease-specific survival of 3 months). Eighteen of 22 cases with interpretable immunohistochemistry results showed loss of expression of core SWI/SNF protein(s) that are expected to result in SWI/SNF complex inactivation as 10 exhibited coloss of ARID1A and ARID1B, 7 loss of SMARCA4, and 1 loss of SMARCB1. Six of 23 cases were MMR-deficient. Two of 20 cases exhibited mutation-type p53 immunoreactivity. Methylation profiles showed coclustering of DDOC/UDOC with UDEC, which collectively were distinct from SCCOHT and HGSC. However, DDOC/UDOC showed an intermediate degree of copy number variation, which was slightly greater, compared with SCCOHT but much less compared with HGSC. Overall, DDOC/UDOC, like its endometrial counterpart, is highly aggressive and is characterized by frequent inactivation of core SWI/SNF complex proteins and MMR deficiency. Its molecular profile overlaps with UDEC while being distinct from SCCOHT and HGSC.

Detection of FOXL2 C134W Mutation Status by a Novel BaseScope In Situ Hybridization Assay is Highly Sensitive and Specific for Adult Granulosa Cell Tumors.

Adult granulosa cell tumors (AGCTs) are a molecularly distinct group of malignant ovarian sex cord-stromal tumors (SCSTs) characterized by a nearly ubiquitous c.402C>G/p.C134W mutation in FOXL2 (hereafter referred to as "C134W"). In some cases, AGCT exhibits marked morphologic overlap with other SCSTs and has an identical immunophenotype, and molecular testing may be necessary to help confirm the diagnosis. However, molecular testing is time consuming, relatively expensive, and unavailable in many pathology laboratories. We describe the development and validation of an in situ hybridization (ISH) custom BaseScope assay for the detection of the FOXL2 C134W mutation. We evaluated 106 ovarian SCSTs, including 78 AGCTs, 9 juvenile granulosa cell tumors, 18 fibromas (cellular and conventional), and 1 SCST, not otherwise specified, as well as 53 epithelial ovarian tumors (42 endometrioid carcinomas and 11 carcinosarcomas) and 1 STK11 adnexal tumor for the presence or absence of FOXL2 wild-type and FOXL2 C134W RNA expression via BaseScope-ISH. Fifty-one tumors had previously undergone DNA sequencing of the FOXL2 gene. Across the entire cohort, the FOXL2 C134W probe staining was positive in 77 of 78 (98.7%) AGCTs. Two of 81 (2.5%) non-AGCTs also showed positive staining, both of which were epithelial ovarian tumors. The assay worked in tissue from blocks >20 years old. There was 100% concordance between the FOXL2 sequencing and BaseScope-ISH results. Overall, assessment of FOXL2 mutation status by custom BaseScope-ISH demonstrated 98.7% sensitivity and 97.5% specificity for the diagnosis of AGCT. BaseScope-ISH for FOXL2 C134W represents a reasonable alternative to sequencing, is quicker and less expensive, and is more easily incorporated than molecular testing into many pathology laboratories. It also has the advantage of requiring less tissue, and the neoplastic cells can be directly visualized on stained sections.

Genomic characterization of DICER1-associated neoplasms uncovers molecular classes.

DICER1 syndrome is a tumor predisposition syndrome that is associated with up to 30 different neoplastic lesions, usually affecting children and adolescents. Here we identify a group of mesenchymal tumors which is highly associated with DICER1 syndrome, and molecularly distinct from other DICER1-associated tumors. This group of DICER1-associated mesenchymal tumors encompasses multiple well-established clinicopathological tumor entities and can be further divided into three clinically meaningful classes designated "low-grade mesenchymal tumor with DICER1 alteration" (LGMT DICER1), "sarcoma with DICER1 alteration" (SARC DICER1), and primary intracranial sarcoma with DICER1 alteration (PIS DICER1). Our study not only provides a combined approach to classify DICER1-associated neoplasms for improved clinical management but also suggests a role for global hypomethylation and other recurrent molecular events in sarcomatous differentiation in mesenchymal tumors with DICER1 alteration. Our results will facilitate future investigations into prognostication and therapeutic approaches for affected patients.

High-Grade Endometrial Stromal Sarcomas With YWHAE::NUTM2 Gene Fusion Exhibit Recurrent CDKN2A Alterations and Absence of p16 Staining is a Poor Prognostic Marker.

High-grade endometrial stromal sarcomas (HGESSs) are aggressive uterine tumors harboring oncogenic fusion proteins. We performed a molecular study of 36 HGESSs with YWHAE::NUTM2 gene fusion, assessing co-occurring genetic events, and showed that these tumors frequently harbor recurrent events involving the CDKN2A locus on chromosome 9p. Using array-based copy number profiling and CDKN2A fluorescence in situ hybridization, we identified homozygous and hemizygous deletions of CDKN2A in 18% and 14% of tumors (n = 22 analyzed), respectively. While all YWHAE-rearranged HGESSs with retained disomy for CDKN2A were immunohistochemically positive for p16INK4 (p16), all tumors with homozygous deletion of CDKN2A showed complete absence of p16 staining. Of the 2 tumors with a hemizygous deletion of CDKN2A, 1 showed diffuse and strong p16 positivity, whereas the other showed complete absence of staining. In the p16-negative case, we did not find intragenic mutations or DNA promoter methylation to explain the p16 protein loss, implicating other mechanisms in the regulation of protein expression. In our cohort, subclonal or complete absence of p16 staining was associated with worse overall survival compared with positive p16 staining (1-year overall survival: 28.6% vs 90.7%, respectively; n = 32; P < .001), with all 7 patients in the p16-negative group having succumbed to their disease within 2 years of diagnosis. Our results suggested CDKN2A alterations as a cooperative driver of tumorigenesis in a subset of HGESSs with the YWHAE::NUTM2 gene fusion and showed p16 to be a potential prognostic marker.

Well-differentiated Sertoli-Leydig Cell Tumors (SLCTs) Are Not Associated With DICER1 Pathogenic Variants and Represent a Different Tumor Type to Moderately and Poorly Differentiated SLCTs.

Sertoli-Leydig cell tumors (SLCTs) are uncommon ovarian sex cord-stromal neoplasms which are currently classified into well, moderately, and poorly differentiated and retiform types. Well-differentiated SLCT is the least common and typically occurs in pure form, whereas moderately and poorly differentiated and retiform types often comprise a morphologic spectrum with an admixture of all 3. DICER1 pathogenic variants are very common in SLCTs but, as far as we are aware, have not been reported in well-differentiated neoplasms, although the number of cases studied is small due to the rarity of this neoplasm. We undertook DICER1 molecular testing in a cohort of 18 well-differentiated SLCTs and show all these to be DICER1 wild-type. None of the cases harbored the p. FOXL2 C134W hotspot mutation. Based upon the DICER1 molecular results, together with morphologic observations, we propose that well-differentiated SLCT is an unrelated neoplasm to the more common moderately/poorly differentiated and retiform SLCTs and is a fundamentally distinct and unrelated tumor type within the ovarian sex cord-stromal tumor family. The implications for tumor nomenclature and recommendations for future tumor classification are discussed within the context of tumors collectively known as SLCTs.

Germline Missense Variants in CDC20 Result in Aberrant Mitotic Progression and Familial Cancer.

CDC20 is a coactivator of the anaphase promoting complex/cyclosome (APC/C) and is essential for mitotic progression. APC/CCDC20 is inhibited by the spindle assembly checkpoint (SAC), which prevents premature separation of sister chromatids and aneuploidy in daughter cells. Although overexpression of CDC20 is common in many cancers, oncogenic mutations have never been identified in humans. Using whole-exome sequencing, we identified heterozygous missense CDC20 variants (L151R and N331K) that segregate with ovarian germ cell tumors in two families. Functional characterization showed these mutants retain APC/C activation activity but have impaired binding to BUBR1, a component of the SAC. Expression of L151R and N331K variants promoted mitotic slippage in HeLa cells and primary skin fibroblasts derived from carriers. Generation of mice carrying the N331K variant using CRISPR-Cas9 showed that, although homozygous N331K mice were nonviable, heterozygotes displayed accelerated oncogenicity of Myc-driven cancers. These findings highlight an unappreciated role for CDC20 variants as tumor-promoting genes. SIGNIFICANCE: Two germline CDC20 missense variants that segregate with cancer in two families compromise the spindle assembly checkpoint and lead to aberrant mitotic progression, which could predispose cells to transformation. See related commentary by Villarroya-Beltri and Malumbres, p. 3432.

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

AIMS: Dedifferentiated 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 RESULTS: The 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. CONCLUSIONS: Our 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.

TRACEBACK: Testing of Historical Tubo-Ovarian Cancer Patients for Hereditary Risk Genes as a Cancer Prevention Strategy in Family Members.

PURPOSE: Tubo-ovarian cancer (TOC) is a sentinel cancer for BRCA1 and BRCA2 pathogenic variants (PVs). Identification of a PV in the first member of a family at increased genetic risk (the proband) provides opportunities for cancer prevention in other at-risk family members. Although Australian testing rates are now high, PVs in patients with TOC whose diagnosis predated revised testing guidelines might have been missed. We assessed the feasibility of detecting PVs in this population to enable genetic risk reduction in relatives. PATIENTS AND METHODS: In this pilot study, deceased probands were ascertained from research cohort studies, identification by a relative, and gynecologic oncology clinics. DNA was extracted from archival tissue or stored blood for panel sequencing of 10 risk-associated genes. Testing of deceased probands ascertained through clinic records was performed with a consent waiver. RESULTS: We identified 85 PVs in 84 of 787 (11%) probands. Familial contacts of 39 of 60 (65%) deceased probands with an identified recipient (60 of 84; 71%) have received a written notification of results, with follow-up verbal contact made in 85% (33 of 39). A minority of families (n = 4) were already aware of the PV. For many (29 of 33; 88%), the genetic result provided new information and referral to a genetic service was accepted in most cases (66%; 19 of 29). Those who declined referral (4 of 29) were all male next of kin whose family member had died more than 10 years before. CONCLUSION: We overcame ethical and logistic challenges to demonstrate that retrospective genetic testing to identify PVs in previously untested deceased probands with TOC is feasible. Understanding reasons for a family member's decision to accept or decline a referral will be important for guiding future TRACEBACK projects.

Neuroectodermal elements are part of the morphological spectrum of DICER1-associated neoplasms.

Many sarcomas with DICER1 pathogenic variants (PVs) exhibit a characteristic morphology, including a subepithelial layer of malignant mesenchymal cells, areas of rhabdomyoblastic differentiation and cartilaginous and/or osseous elements. We report 5 DICER1-associated neoplasms (1 moderately to poorly differentiated Sertoli Leydig cell tumour and 4 sarcomas) containing variable amounts of neuroectodermal elements. The neoplasms predominantly involved or were in close proximity to the female genital tract (ovary, uterine corpus, abdominal and pelvic cavity) and occurred in females aged 14 months to 54 years. The neuroectodermal elements were characterised by solid and tubular/rosette-like patterns and variable immunoreactivity with SALL4 and neuroendocrine markers. In some cases, the neuroectodermal component was focal while in others it was exclusive. In one case, the focal neuroectodermal component within an ovarian Sertoli Leydig cell tumour resulted in extraovarian metastasis. In reporting these cases, we suggest that neuroectodermal elements, including pure neuroectodermal tumours, are part of the morphological spectrum of DICER1-associated neoplasms. It is important that pathologists recognize that a neuroectodermal component (often admixed with other elements) may be a feature of such neoplasms. This will facilitate appropriate tumour and/or germline testing which could lead to the identification of germline DICER1 PVs (DICER1 syndrome). Three of the patients we report were subsequently shown to have a germline DICER1 PV.

An Unusual Enteric Yolk Sac Tumor: First Report of an Ovarian Germ Cell Tumor Associated With a Germline Pathogenic Variant in DICER1.

A variety of unusual tumors are associated with both germline and somatic DICER1 pathogenic variants (PVs), including, in the female genital tract, embryonal rhabdomyosarcoma at various sites and ovarian Sertoli-Leydig cell tumor. There have been occasional reported cases of ovarian germ cell tumors [mainly yolk sac tumor (YST)] harboring DICER1 PVs but, as far as we are aware, none of these has been proven to have a germline provenance. We report an unusual enteric variant of ovarian YST in a 28-yr-old woman associated with a germline PV c.901C>T (p.Gln301Ter) in exon 7 of DICER1, accompanied by a somatic (YST-only) hotspot mutation: c.5437G>A, p.E1813K. To our knowledge, this is the first report of an ovarian germ cell tumor associated with a germline DICER1 PV. We review other reported cases of ovarian germ cell tumor with DICER1 PVs and discuss the differential diagnosis of this unusual variant of YST which was originally diagnosed as a mucinous adenocarcinoma.

Bronchus-like Structures in Ovarian Teratomas: Report of a Series of a Previously Unreported Phenomenon With Potential For Misdiagnosis.

We report 10 cases of a previously undescribed lesion within ovarian teratomas which we designate bronchus-like structures. The lesions occurred in patients aged 16 to 56 yr (mean: 36) and involved the left ovary (n=5) or right ovary (n=5). Nine cases were mature teratomas (dermoid cysts/mature cystic teratomas or mature solid teratomas), 1 with somatic malignant transformation, and 1 was an immature teratoma. The bronchus-like structures ranged in size from 2.5 to 10 mm and were unifocal (7 cases) or multifocal (3 cases). The morphology was relatively constant in all cases and characterised by a well-formed bronchus surrounded by glandular structures, some of which were dilated, separated by stroma containing a variable amount of smooth muscle. In all but 1 case, a proportion of the glands contained abundant foamy cytoplasm. There was little or no nuclear atypia or mitotic activity. At low-power, the glands often had a somewhat "infiltrative" appearance and one case was originally diagnosed as a "pulmonary-type" adenocarcinoma arising in a dermoid cyst. In all cases, there was diffuse staining of the bronchus and glands with TTF1 and Napsin A, confirming the cell lineage. Follow-up in 4 cases (18-130 mo; median: 64 mo) showed no evidence of recurrence; 1 patient died from an unrelated malignancy. In reporting this apparently rare but possibly underrecognized benign lesion arising within ovarian teratomas, we discuss the differential diagnosis and stress that pathologists should be aware of this phenomenon in order to avoid an erroneous diagnosis of malignancy.

TSC2-mutant uterine sarcomas with JAZF1-SUZ12 fusions demonstrate hybrid features of endometrial stromal sarcoma and PEComa and are responsive to mTOR inhibition.

Uterine perivascular epithelioid cell tumor (PEComa) is a rare mesenchymal neoplasm that occasionally shares morphologic and immunohistochemical overlap with low- and high-grade endometrial stromal sarcoma (LGESS and HGESS). In this study, we sought to characterize the clinical, morphologic, genetic, and epigenetic features of five uterine sarcomas that display histologic features of LGESS, HGESS, and PEComa. All tumors demonstrated epithelioid cells often associated with a low-grade spindled component resembling LGESS, with both regions expressing CD10, ER, PR, variable HMB45, and Melan-A immunoreactivity, and strong cathepsin K and pS6 expression. Targeted massively parallel sequencing analysis revealed the presence of somatic TSC2 mutations in all five cases, of which four harbored concurrent or consecutive JAZF1-SUZ12 gene fusions. Unsupervised hierarchical clustering analysis of methylation profiles of TSC2-mutant uterine sarcomas (n = 4), LGESS (n = 10), and HGESS (n = 12) demonstrated two clusters consisting of (1) all LGESS and TSC2-mutant uterine sarcomas and (2) all HGESS. KEGG pathway analysis detected methylation differences in genes involved in PI3K/AKT, calcium, and Rap1 signaling. TSC2-mutant uterine sarcomas were responsive to hormone suppression, and mTOR inhibition demonstrated clinical benefit in four patients with these neoplasms. Our results suggest that these tumors represent histologically distinctive LGESS with TSC2 mutations. TSC2 mutations and JAZF1-SUZ12 fusion may help diagnose these tumors and possibly direct effective treatment.

Endometrial Stem/Progenitor cell (ES/PC) Marker Expression Profile in Adenosarcoma and Endometrial Stromal Sarcoma.

BACKGROUND: The uterus is one of the most dynamic organs in the human body, and this dynamic homeostasis is supported by endometrial stem/progenitor cells (ES/PCs), which are heterogeneous in their phenotype and degree of differentiation. ES/PCs are generally localized in the endometrial stroma, the site of origin for adenosarcoma and endometrial stromal sarcoma (ESS). Subsets of ESSs and adenosarcomas harbor SUZ12 or DICER1 gene alterations, two genes with roles in embryonic stem cell biology. However, the possible contribution of ES/PCs to tumorigenesis is unexplored. METHOD: We examined the expression of eleven ES/PC markers, along with three proteins expressed in the mature endometrial stroma (ER, PR and CD10) in 60 uterine tumors (24 low-, 11 high-grade ESS, 25 adenosarcomas). Protein expression profiles were assessed by unsupervised hierarchical clustering. miRNA expression profiles were examined in a subset of adenosarcoma with/without DICER1 mutations, using the NanoString platform. RESULTS: ES/PC markers were variably expressed, and the tumors exhibited limited immunophenotypic resemblance to different ES/PCs. Within the ESSs, the ES/PC marker clustering pattern was prognostic for both overall and disease-free survival. Comparing adenosarcomas and ESSs, most high-grade ESSs clustered with one another, while low-grade ESSs and adenosarcomas tended to cluster with one another. Among the adenosarcomas, the miRNA expression profiles were varied with respect to the DICER1 mutation status, with pathway analysis pointing to dysregulated signal transduction and stem cell biology. CONCLUSIONS: ESSs and adenosarcomas exhibit varying immunophenotypic resemblance to ES/PCs. These expression profiles have prognostic implications and may be genetically driven.

Lynch syndrome associated endometrial carcinomas in Western Australia: an analysis of universal screening by mismatch repair protein immunohistochemistry.

BACKGROUND: In 2016 universal screening with mismatch repair protein immunohistochemistry in all newly diagnosed endometrial carcinomas was introduced in Western Australia. OBJECTIVE: To compare the prevalence of Lynch syndrome associated endometrial carcinomas between 2016 and 2019 with a historical control (2015). Additionally, to compare the number of cases appropriately referred for genetic assessment. METHODS: A cross-sectional study of cases presented at the Western Australia gynecologic oncology tumor board was carried out. The primary outcome was the prevalence of Lynch syndrome associated endometrial carcinomas. A secondary outcome was the number of cases appropriately referred for genetic assessment. The following variables were extracted: date of birth; age at diagnosis; vital status; tumor mismatch repair protein expression status (retained or lost) and if lost, the specific mismatch repair protein deficiency; patients who were referred to a genetic clinic; and family history, if recorded. Data were collected from the clinical databases of the Familial Cancer Program at Genetic Services of Western Australia and WOMEN Center, to determine whether patients were appropriately referred for genetic evaluation and to ascertain the results of genetic testing. RESULTS: Between 2016 and 2019, there were 1040 new endometrial carcinomas. Tumors of 883 (85%) patients underwent mismatch repair protein immunohistochemistry compared with 117 of 199 patients (59%) in 2015 (χ2 73.14, p<0.001). Of 883 tumors tested, 242 (27%) showed loss of mismatch repair protein expression. In 2015, 30 (26%) tumors of 117 tested showed loss of mismatch repair protein expression. During the 4 years of universal screening, 13 (1.5%) of 883 patients screened were diagnosed with Lynch syndrome compared with 2 (1.7%) of 117 in 2015 (Fisher's exact test 0.04, p=0.69). In 2015, 11 (37%) of 30 patients with loss of mismatch repair protein expression were not referred for genetic assessment compared with 36 (17%) of 209 patients in the universal screening group (χ2 6.28, p=0.02). No cases of Lynch syndrome were diagnosed in patients aged over 70 years. CONCLUSIONS: Universal immunohistochemical screening did not increase the proportion of Lynch syndrome associated endometrial carcinomas identified, although the study was underpowered to detect small differences. There was an improvement in appropriate referrals for genetic assessment.

Loss of ARID1B and SMARCB1 expression are specific for the diagnosis of dedifferentiated/undifferentiated carcinoma in tumours of the upper gynaecological tract and cervix.

AIMS: Genomic inactivation of ARID1B in ARID1A-inactivated tumour and genomic inactivation of SMARCB1 represent two recurrent mechanisms, core SWItch/sucrose non-fermentable (SWI/SNF) complex inactivation, that are associated with de-differentiation in endometrial carcinoma. Approximately one-third of dedifferentiated/undifferentiated endometrial carcinomas (DDEC/UEC) show loss of ARID1B expression with a minor subset showing loss of SMARCB1 expression, but little is known regarding the specificity of ARID1B or SMARCB1 loss in gynaecological tract tumours in general. The aim of this study was to examine the frequency of ARID1B and SMARCB1 loss by immunohistochemistry in a series of gynaecological tract epithelial/mesenchymal neoplasms. METHODS AND RESULTS: We evaluated 1849 tumours that included 748 endometrial carcinomas, 101 uterine carcinosarcomas/adenosarcomas, 64 uterine sarcomas, 221 cervical carcinomas and 715 ovarian carcinomas/borderline tumours by tissue microarrays (TMA). We observed ARID1B loss in 35 of 86 (41%) and SMARCB1 loss in three of 86 (3%) DDEC/UEC, but not in any other uterine tumour types examined. ARID1B-deficient DDEC/UEC also showed concurrent loss of ARID1A expression. All SMARCB1-deficient tumours showed loss of MLH1 and PMS2, while 29 of 35 ARID1B-deficient tumours showed loss of MLH1 and PMS2 or loss of MSH6. All ovarian carcinomas/borderline tumours and cervical carcinomas showed intact expression of ARID1B and SMARCB1. CONCLUSION: Our findings indicate that the loss of expression of ARID1B or SMARCB1 by immunohistochemistry is highly specific for undifferentiated carcinoma among tumours of the upper gynaecological tract and cervix, and therefore can be used to identify these highly aggressive malignant tumours.

p53 immunohistochemical analysis of fusion-positive uterine sarcomas.

AIMS: Uterine sarcomas can be grouped into tumours with pathognomonic genetic fusions such as low-grade endometrial stromal sarcoma (LGESS), high-grade endometrial stromal sarcoma (HGESS), and inflammatory myofibroblastic tumour (IMT), and tumours lacking genetic fusions such as leiomyosarcoma (LMS) and undifferentiated uterine sarcoma (UUS). Members of the latter group frequently harbour TP53 mutations. The aim of this study was to evaluate TP53 mutations by the use of immunohistochemistry in fusion-positive uterine sarcomas. METHODS AND RESULTS: We performed p53 immunohistochemical staining on 124 uterine sarcomas harbouring genetic fusions and 38 fusion-negative LMSs and UUSs. These included 41 HGESSs with YWHAE, BCOR and BCORL1 fusions/rearrangements, 13 IMTs with ALK fusion, 12 sarcomas with NTRK1/3 fusion, three sarcomas with PDGFB fusion, and 55 LGESSs with JAZF1, SUZ12 and PHF1 fusions/rearrangements. All HGESSs, LGESSs, IMTs and sarcomas with PDGFB fusion showed wild-type p53 expression. Among NTRK1/3-positive sarcomas, a TPR-NTRK1-positive sarcoma with nuclear pleomorphism showed mutation-type p53 expression. The remaining 11 NTRK1/3-positive sarcomas showed wild-type p53 expression, except for the subclonal p53 mutation-type staining in a minor pleomorphic focus of an NTRK3-positive sarcoma. Twenty-one of 27 (78%) LMSs and six of nine (67%) UUSs showed mutation-type p53 expression. CONCLUSION: p53 immunohistochemistry may be considered in the initial work-up of a uterine sarcoma, as mutation-type staining would make a fusion-positive sarcoma very unlikely. Mutation-type p53 expression, however, can be seen in a small subset of NTRK1/3-positive sarcomas showing pleomorphic round/ovoid cell histology, which may represent a mechanism of progression in these tumours.

Uterine plexiform tumourlets: multifocal and solitary cases with subsets expressing melanocytic markers.

AIMS: Uterine plexiform tumourlets are traditionally regarded as microscopic epithelioid leiomyomas. They are typically solitary incidental findings, but may be multifocal (plexiform leiomyomatosis). We aim to report novel immunohistochemical and morphological findings, specifically the presence of spindled and epithelioid cell nodules, in these lesions. METHODS AND RESULTS: Three cases of plexiform leiomyomatosis and 16 solitary plexiform tumourlets were included. Two cases of plexiform leiomyomatosis and four solitary plexiform tumourlets demonstrated spindled and epithelioid cell nodules which, in one of the former cases, formed expansile masses up to 15 mm. The nodules demonstrated mild cytological atypia and occasional mitotic activity, and they were associated with a myxoid stroma and a lymphohistiocytic infiltrate which imparted a granulomatous appearance to the microscopic lesions. The plexiform tumourlets (solitary and multifocal) consistently expressed desmin, smooth muscle actin, ER and PR, and they commonly co-expressed melanocytic and perivascular epithelioid cell (PEC) markers HMB45, MiTF and cathepsin K. The spindled and epithelioid cell nodules were generally negative for myoid markers and hormone receptors, but expressed p16, cyclin D1 and TFE3. All lesions tested were negative for cytokeratin, S100, melanA, inhibin, EMA, ALK and BCOR; fluorescence in-situ hybridisation was negative for ALK, TFE3 and BCOR rearrangements in one of the larger spindled and epithelioid cell nodules. CONCLUSIONS: Plexiform tumourlets commonly co-express myoid and melanocytic markers and may represent part of the spectrum of gynaecological PEC-related lesions. Some cases are associated with spindled and epithelioid cell nodules that could potentially mimic other uterine myxoid neoplasms.