Endometrial Stromal Neoplasms Are Immunoreactive with WT-1 Antibody

A review of the directly sampled endometrial cytology on LBC samples: Classification, microscopic criteria and beyond

The Yokohama System for Reporting Endometrial Cytology (TYS) has been proposed by an expert meeting under the auspices of the International Academy of Cytology (IAC) in May 2016 at the IAC in Yokohama. Since its introduction, the TYS has been receiving worldwide acceptance, and this review aims to assess its global impact. The adoption of endometrial cytology as a diagnostic procedure has been hampered in the past by difficulties arising in interpreting the cellular findings due to a number of factors (such as excess blood, cellular overlapping and the complex physiology of endometrium). Recently, the use of liquid-based cytology (LBC), with its ability to remove blood and mucus and to distribute cells uniformly in a thin layer on the slide, has provided an opportunity to re-evaluate the role of endometrial cytology. LBC is a useful tool in the cytologic diagnosis and follow-up of endometrial abnormalities, which remains complementary to the emerging molecular diagnostic cytopathology. The study of LBC from endometrial cytology could be challenging since it is affected by numerous look-alikes and diagnostic pitfalls. This review discusses these various entities and takes into consideration the ancillary techniques that may be useful in the diagnostic procedure. In conclusion, our review of the published data suggests that the TYS is a valid classification scheme that has been widely accepted by cytopathologists globally, is highly reproducible and makes a valuable contribution to clinical therapeutic management. At present, molecular cytopathology is a rapidly evolving field of modern cytopathology, which underlines the effective interplay between genomics and cytology. This review aims to provide a comprehensive review of the drawbacks of endometrial cytopathology, particularly in terms of endometrial cancer diagnosis and molecular testing.

Histopathological Evaluation and Molecular Diagnostic Tests for Peritoneal Metastases with Unknown Primary Site-a Review

Cancer of unknown primary (CUP) is a well-studied entity with guidelines available for the management of patients with CUP. The peritoneum represents one of the metastatic sites in CUP, and peritoneal metastases (PM) could present as CUP. PM of unknown origin remains a poorly studied clinical entity. There is only one series of 15 cases, one population-based study, and few other case reports on this subject. Studies on CUP, in general, cover some common tumour histological types like adenocarcinomas and squamous carcinomas. Some of these tumours may have a good prognosis though majority have high-grade disease with a poor long-term outcome. Some of the histological tumour types commonly seen in the clinical scenario of PM like mucinous carcinoma have not been studied. In this review, we divide PM into five histological types-adenocarcinomas, serous carcinomas, mucinous carcinomas, sarcomas and other rare varieties. We provide algorithms to identify the primary tumour site using immunohistochemistry when imaging, and endoscopy fails to establish the primary tumour site. The role of molecular diagnostic tests for PM or unknown origin is also discussed. Current literature on site-specific systemic therapy based on gene expression profiling does not show a clear benefit of this approach over empirical systemic therapies.

Low-grade endometrial stromal sarcoma-like tumors in male with JAZF1 gene fusions

Low-grade endometrial stromal sarcoma (ESS) is a hormone-responsive low-grade sarcoma typically occurring in the uterine corpus in women. Their genetic hallmarks are recurrent gene fusions involving JAZF1, partnering with either SUZ12 gene or less commonly with PHF1. Low-grade ESS-like sarcoma, or endometrioid stromal sarcoma, is exceptionally rare in males and has been reported to date only in two cases, one in the paratesticular area and the other of prostatic stromal origin. We report herein two new cases of low-grade ESS-like sarcoma in male patients, one presenting as a periprostatic/peri-rectal mass with a JAZF1-GLI3 fusion, while the other as a paratesticular mass with a JAZF1-PHF1 fusion. As the GLI3 fusion appeared novel, we searched the transcriptional signature of 35 low-grade ESS from our archives and found a similar JAZF1-GLI3 fusion in a low-grade ESS arising from the uterine corpus, supporting a common pathogenesis. Histopathologically, both cases demonstrate cellular, monotonous proliferation of ovoid to fusiform cells with a background of arteriolar vascular network. Immunohistochemically, the neoplastic cells express ER, PR, and CD10, similar to ESS. One case also expresses diffuse and strong AR. On follow-up, the patient with the periprostatic mass recurred 2 years after initial surgery with peritoneal "sarcomatosis." We describe the salient diagnostic morphologic, immunohistochemical, and molecular features and discuss the differential diagnosis and possible pathogenesis of this unusual entity.

Carcinoma arising within sciatic nerve endometriosis: a case report

Endometriosis is a common condition with significant morbidity. There have been case reports of endometrial deposits affecting the sciatic nerve. Sciatic nerve endometriosis presents with cyclical sciatica and is often difficult to diagnose as it mimics many other causes of sciatica. We report the first case of histological proven endometrial carcinoma arising in a pre-existing sciatic nerve endometriosis. This was initially managed with radiotherapy however symptoms persisted and she opted to have surgery with the aim of better symptom control and long-term prognosis.

P16, Ki67, P53, and WT1 Expression in Uterine Smooth Muscle Tumors: An Adjunct in Confirming the Diagnosis of Malignancy in Ambiguous Cases

The diagnosis of uterine smooth muscle tumors is sometimes difficult, as these tumors may show worrisome features, suspicious for but not diagnostic of malignancy. The recommended immunohistochemical panel in this setting is currently under debate. In this study, we aimed to find a panel of immunohistochemical stains that would be helpful in determining the correct diagnosis in ambiguous uterine smooth muscle tumors, with an emphasis on investigating the possible usefulness of the WT1 antibody. Uterine leiomyomas were found to be immunoreactive with WT1. Since a previous study reported on the lack of immunoreactivity of uterine leiomyosarcomas with WT1, we speculated that WT1 might be useful in this setting. We retrospectively reviewed the medical charts and slides of 91 patients: 22 with leiomyosarcoma, 15 with smooth muscle tumor of uncertain malignant potential, and 54 with leiomyoma. Immunohistochemical stains for WT1, p16, p53, and Ki67 were performed on each case. We found that immunoreactivity with p16 and Ki67 (>40% and >10% of the tumor cells, respectively) and loss of nuclear expression of WT1 (<10% of the tumor cells) were significantly more common in leiomyosarcomas (all P<0.001). Mutated p53 immunohistochemical staining pattern was significantly more prevalent in leiomyosarcomas than in leiomyomas (P<0.001). Thus, in diagnostically challenging uterine smooth muscle tumors, we recommend using an immunohistochemical panel composed of Ki67, p16, p53, and WT1. A positive result in either of the former 2 (p16 >40% and/or Ki67 >10%) has the strongest association with leiomyosarcoma (sensitivity: 95.5%, specificity=88.9%, positive predictive value=77.8%, negative predictive value=98.0%).

Update on Endometrial Stromal Tumours of the Uterus

Endometrial stromal tumours (ESTs) are rare, intriguing uterine mesenchymal neoplasms with variegated histopathological, immunohistochemical and molecular characteristics. Morphologically, ESTs resemble endometrial stromal cells in the proliferative phase of the menstrual cycle. In 1966 Norris and Taylor classified ESTs into benign and malignant categories according to the mitotic count. In the most recent classification by the WHO (2020), ESTs have been divided into four categories: Endometrial Stromal Nodules (ESNs), Low-Grade Endometrial Stromal Sarcomas (LG-ESSs), High-Grade Endometrial Stromal Sarcomas (HG-ESSs) and Undifferentiated Uterine Sarcomas (UUSs). ESNs are clinically benign. LG-ESSs are tumours of low malignant potential, often with indolent clinical behaviour, with some cases presented with a late recurrence after hysterectomy. HG-ESSs are tumours of high malignant potential with more aggressive clinical outcome. UUSs show high-grade morphological features with very aggressive clinical behavior. With the advent of molecular techniques, the morphological classification of ESTs can be integrated with molecular findings in enhanced classification of these tumours. In the future, the morphological and immunohistochemical features correlated with molecular categorisation of ESTs, will become a robust means to plan therapeutic decisions, especially in recurrences and metastatic disease. In this review, we summarise the morphological, immunohistochemical and molecular features of ESTs with particular reference to the most recent molecular findings.

Molecular Classification of Endometrial Stromal Sarcomas Using RNA Sequencing Defines Nosological and Prognostic Subgroups with Different Natural History

A series of 42 patient tumors diagnosed as endometrial stromal sarcoma (ESS) based on the morphology but negative for JAZF1 and/or YWHAE rearrangement in FISH was analyzed by RNA-sequencing. A chromosomal rearrangement was identified in 31 (74%) of the cases and a missense mutation in known oncogenes/tumor suppressor genes in 11 (26%). Cluster analyses on the expression profiles from this series together with a control cohort composed of five samples of low grade ESS harboring a JAZF1-SUZ12 fusion, one high grade ESS harboring a BCOR-ITD, two uterine tumors resembling ovarian sex cord tumors, two samples each of uterine leiomyoma and leiomyosarcomas and a series of BCOR-rearranged family of tumor (n = 8) indicated that tumors could be gather in three distinct subgroups: one mainly composed of BCOR-rearranged samples that contained seven ESS samples, one mainly composed of JAZF1-fused ESS (n = 15) and the last composed of various molecular subtypes (n = 19). These three subgroups display different gene signatures, different in silico cell cycle scores and very different clinical presentations, natural history and survival (log-rank test, p = 0.004). While YWHAE-NUTM2 fusion genes may be present in both high and low grade ESS, the high-grade presents with additional BCOR or BCORL1 gene mutations. RNAseq brings clinically relevant molecular classification, enabling the reclassification of diseases and the guidance of therapeutic strategy.

Diagnostic and Prognostic Role of WT1 Immunohistochemical Expression in Uterine Carcinoma: A Systematic Review and Meta-Analysis across All Endometrial Carcinoma Histotypes

Background: The diagnostic role of Wilms’ tumor 1 (WT1) is well known in gynaeco-pathological setting, since it is considered a specific marker of serous histotype and adnexal origin. Moreover, its oncogenic role has been recently highlighted in many cancers and it has also been regarded as a promising target antigen for cancer immunotherapy. However, the relationship between its expression and prognostic role in uterine cancer remains unclear. We analyzed the diagnostic and prognostic role of WT1 expression in patients with uterine carcinoma by completing a search using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines and the PICOS (Participants, Intervention, Comparison, Outcomes, Study Design) model through PubMed, Scopus and Web of Science databases to identify studies that fit our search criteria. The objective of the current meta-analysis was to investigate the diagnostic and prognostic role of WT1 expression in patients with uterine carcinoma. Materials and Methods: A literature search was performed of the PubMed, Scopus, and Web of Science databases for English-language studies published from January 2000 to April 2020. Studies were considered eligible if they evaluated the WT1 expression in uterine carcinoma. Results: In total, 35 articles were identified that used uterine carcinoma criteria and provided data for 1616 patients. The overall rate of WT1 expression in uterine carcinoma was 25%. The subgroup analysis of uterine cancer types revealed that WT1 was expressed differently among different histotypes (endometrioid, clear cell, serous carcinoma and carcinosarcoma). Discussion and Conclusions: The WT1 immunohistochemical expression is not limited to serous histotype and/or ovarian origin. In fact, a significant proportion of endometrial adenocarcinomas can also show WT1 immunoreactivity. Moreover, our study suggests that WT1 may be a potential marker to predict the prognosis of patients with uterine cancer, but more studies are needed to confirm its role in clinical practice.

A Diagnostic Approach to Endometrial Cytology by Means of Liquid-Based Preparations

The adoption of endometrial cytology as a diagnostic procedure has been hampered in the past by difficulties arising in interpreting the cellular findings due to a number of factors (such as excess blood, cellular overlapping, and the complex physiology of endometrium). Recently, the use of liquid-based cytology (LBC), with its ability to remove blood and mucus and to distribute cells uniformly in a thin layer on the slide, has provided an opportunity to reevaluate the role of endometrial cytology. LBC samples are easier to screen compared to conventional ones, due to a smaller screening area and an excellent quality of cell preparations. LBC by using peculiar cytoarchitectural features is a useful tool in the cellular diagnosis and follow-up of abnormalities, which, however, remains complementary to histopathology and to the emerging molecular diagnostic cytopathology. This review discusses these various entities and takes into consideration the ancillary techniques that may be useful in the diagnostic procedure. Herein, we also summarize the process and rationale by which updates were made to the standardized terminology in 2018 and outline the contents of the new Bethesda-style classification (the Yokohama system) for the endometrial cytology.

Proliferative Lesions of the Endometrium of 50 Four-Toed Hedgehogs ( Atelerix albiventris)

Uteri from 50 four-toed hedgehogs ( Atelerix albiventris) with clinical signs of uterine disease were histopathologically examined. Sixteen animals (32%) were diagnosed with endometrial hyperplasia, 7 animals (14%) were diagnosed with endometrial polyp, and 27 animals (54%) were diagnosed with endometrial neoplasia. The mean ages of the animals with endometrial hyperplasia, polyp, and neoplasia were 28.7 months, 29.4 months, and 25.2 months, respectively. The neoplasms were classified into 7 endometrial mixed tumors, 12 endometrial stromal nodules, and 8 endometrial stromal sarcomas. However, the endometrial stromal nodules and endometrial stromal sarcomas often developed within or were contiguous with an endometrial polyp or mixed tumor. Interestingly, the stromal tumors and the stromal components of the endometrial polyp and mixed tumor displayed extraendometrial differentiation (eg, into adipocytes, granular cells, smooth muscle cells, and osteoid tissue). The endometrial stromal sarcomas exhibited severe cellular atypia and invaded subendometrial tissue. Immunohistochemical examinations demonstrated that the stromal cells of the hyperplastic lesions as well as the neoplastic lesions were positive for CD10, the progesterone receptor, and Wilms tumor 1. The four-toed hedgehog develops unique uterine neoplasms that are mainly composed of endometrial stromal cells and probably arise from endometrial polyps and/or mixed tumors.

Immunohistochemistry in Gynecologic Pathology: An Example-Based Practical Update

CONTEXT

- Immunohistochemical stains are routinely applied in the pathology diagnostic workup of gynecologic lesions. The rapidly expanding repertoire of available markers helps in refining the diagnostic criteria for each disease entity; however, limitations and pitfalls exist.

OBJECTIVE

- To provide a practical, relevant update on the use of immunohistochemistry for commonly encountered differential diagnoses in gynecologic pathology.

DATA SOURCES

- Literature review and authors' diagnostic experience.

CONCLUSIONS

- Immunohistochemistry is a helpful adjunct tool in gynecologic pathology. Although the primary application is in the diagnostic workup, novel prognostic and predictive markers, and immunostains to screen for genetic cancer syndromes, have also been recently introduced in the field.

Spindle Cell Epithelioma of the Vagina

Spindle cell epitheliomas of the vagina are rare benign tumors of uncertain histogenesis. It has been hypothesized that they originate from a pluripotent cell population. Here, we report 2 cases of spindle cell epitheliomas of the vagina. Both patients presented with a painless vaginal nodule. The resected lesions were solid, well circumscribed, and composed of a proliferation of epithelioid or epithelial cells admixed with spindle cells without atypia. The 2 cellular populations expressed epithelial and mesenchymal markers. Based on these morphologic and immunohistochemical findings, a diagnosis of spindle cell epithelioma was rendered in both cases. Furthermore, we describe for the first time the expression of WT-1 (Wilms’ tumor protein 1) and calretinin in addition to the previously defined immunohistochemical profile.

Endometrial stromal tumors: the new WHO classification

Endometrial stromal tumors are rare uterine mesenchymal neoplasms that have intrigued pathologists for years, not only because they commonly pose diagnostic dilemmas, but also because the classification and pathogenesis of these tumors has been widely debated. The current World Health Organization recognizes 4 categories of endometrial stromal tumor: endometrial stromal nodule (ESN), low-grade endometrial stromal sarcoma (LG-ESS), high-grade endometrial stromal sarcoma (HG-ESS), and undifferentiated uterine sarcoma (UUS). uterine sarcoma. These categories are defined by the presence of distinct translocations as well as tumor morphology and prognosis. Specifically, the JAZF1-SUZ12 (formerly JAZF1-JJAZ1) fusion identifies a large proportion of ESN and LG-ESSs, whereas the YWHAE-FAM22 translocation identifies HG-ESSs. The latter tumors appear to have a prognosis intermediate between LG-ESS and UUS, which exhibits no specific translocation pattern. This review (1) presents the clinicopathologic features of endometrial stromal tumors; (2) discusses their immunophenotype; and (3) highlights the recent advances in molecular genetics which explain their pathogenesis and lend support for a new classification system.

Wilms' tumor gene 1 immunotherapy in pelvic gynecological malignancies

Pelvic gynecological malignancies account for 6% of all cancers. In the relapsed state, classical treatments are limited. There is an urgent need for new and personalized treatment. Wilms' tumor gene 1 (WT1) is the most important tumor-associated antigen. Although highly present in gynecological tumors, active immunotherapy against it is still underexplored. This review gives an insight into the importance of WT1 in pelvic gynecological malignancies and the first taken steps into the world of WT1 immunotherapy.

Diagnostic use of immunohistochemistry in uterine mesenchymal tumors

Immunohistochemistry may be helpful in the diagnosis of mesenchymal uterine tumors. This article reviews the immunoreactions used most frequently in the diagnosis of uterine smooth muscle tumors, endometrial stromal tumors, undifferentiated endometrial sarcomas, UTROSCTs, PEComas, adenomyomas, adenosarcomas and carcinosarcomas.

Recent developments in uterine mesenchymal neoplasms

Smooth muscle and endometrial stromal tumours represent the two most common uterine mesenchymal neoplasms that may present diagnostic dilemmas for the practising surgical pathologist. Recent changes in morphological and staging criteria, as well as the discovery of new immunohistochemical markers, have improved the diagnosis and classification of these tumours. We highlight the difficulty in distinguishing tumour cell necrosis from infarct-type necrosis and the limited utility of p16 immunohistochemical expression in the diagnosis of leiomyosarcoma. We also discuss the controversial use of mitotic activity and necrosis as prognostic factors in endometrial stromal sarcomas. Emerging genetic information has also greatly expanded our understanding of 'sarcomagenesis' in both tumour types and may provide insight into potential therapeutic targets for the treatment of leiomyosarcoma and endometrial stromal sarcomas, harboring MED12 (mediator complex subunit 12) mutations and recurrent gene rearrangements, respectively. In this review, we discuss the core updates in the diagnosis and classification of uterine leiomyosarcomas and endometrial stromal sarcomas, highlighting new and important molecular genetic findings that may drive pathogenesis.

The role of liquid-based preparation in the evaluation of endometrial cytology

OBJECTIVE

Liquid-based preparation (LBP) of the endometrial lesions is an important diagnostic tool for a variety of endometrial abnormalities because of its simplicity and high quali-quantitative diagnostic yield. We aimed to investigate the LBP method for endometrial cytology to evaluate both benign and abnormal endometrial lesions.

STUDY DESIGN

LBP is a semiautomated methodology that has recently become widely available and has gained popularity as a method of collecting and processing both gynecologic and nongynecologic cellular specimens.

RESULTS

Some peculiar endometrial cytoarchitectural features were described using LBPs. These were advantageous to screen as compared to conventional slides due to a smaller screening area and an excellent quality of cell preparations.

CONCLUSIONS

LBP is a useful tool in the cellular diagnosis and follow-up of endometrial abnormalities, which remains complementary to the emerging molecular diagnostic cytopathology. The study of LBPs from endometrial cytology could be challenging since it is affected by numerous look-alikes and diagnostic pitfalls. This review discusses these various entities and takes into consideration the ancillary techniques that may be useful in the diagnostic procedure.

WT1 expression in the female genital tract

The Wilms tumor gene 1 (WT1) has been reported in normal tissues and many neoplasms of the female genital tract. This review discusses WT1 expression in the female genital tract and its potential utility in the differential diagnosis of neoplasms that occur at this location. WT1 is of value in the differential diagnosis of synchronous serous carcinomas arising in the ovary/fallopian tube/peritoneum and endometrium, as strong WT1 positivity in both tumors points toward an extrauterine origin. In addition, WT1 can be used to distinguish sex cord stromal tumors (WT1 positive) from endometrioid carcinomas (OECs). WT1 expression is not helpful in the differential diagnosis of ovarian serous carcinomas (OSCs) and transitional carcinomas, as both are typically positive and has limited value in the distinction of serous tumors arising in the ovary/fallopian tube/peritoneum from mesotheliomas. WT1 is also not helpful to differentiate small cell carcinoma of hypercalcemic type from juvenile granulosa cell tumor, a common diagnostic problem. Intra-abdominal desmoplastic round cell tumor reacts to WT1 (C-terminal) in contrast to all other tumors discussed which helps to separate this rare tumor from most other small round cell tumors that may involve, primarily or secondarily, the ovary with the exception of small cell carcinoma of hypercalcemic type that typically reacts with the N-terminal of WT1.

Characterization of the molecular differences between ovarian endometrioid carcinoma and ovarian serous carcinoma

The histopathological diagnosis of high-grade endometrioid and serous carcinoma of the ovary is poorly reproducible under the current morphology based classification system, especially for anaplastic, high-grade tumours. The transcription factor Wilms' tumour-1 (WT1) is differentially expressed among the gynaecological epithelia from which epithelial ovarian cancers (EOCs) are believed to originate. In EOCs, WT1 protein is observed in the majority of serous carcinomas and in up to 30% of endometrioid carcinomas. It is unclear whether the latter is a reflection of the actual incidence of WT1 protein expression in endometrioid carcinomas, or whether a significant number of high-grade serous carcinomas have been misclassified as endometrioid carcinoma. Several genetic aberrations are reported to occur in EOCs. These include mutation of the TP53 gene, aberrant activation of beta-catenin signalling and loss of PTEN protein expression, among others. It is unclear whether these aberrations are histotype-specific. The aim of this study was to better define the molecular characteristics of serous and endometrioid carcinomas in an attempt to address the problems with the current histopathological classification methods. Gene expression profiles were analysed to identify reproducible gene expression phenotypes for endometrioid and serous carcinomas. Tissue microarrays (TMA) were used to assess the incidence of TP53, beta-catenin and PTEN aberrations in order to correlate their occurrence with WT1 as an immunohistochemistry based biomarker of serous histotype. It was found that nuclear WT1 protein expression can identify misclassified high-grade endometrioid carcinomas and these tumours should be reassigned to serous histotype. Although low-grade endometrioid carcinomas rarely progress to high-grade carcinomas, a combined WT1-negative, TP53-positive immunophenotype may identify an uncommon high-grade subtype of ovarian endometrioid carcinoma. GEO database: array data accession number GSE6008.

Evaluation of podocyte lesion in patients with diabetic nephropathy: Wilms' tumor-1 protein used as a podocyte marker

INTRODUCTION

The reduction of podocyte number and density per glomerulus has been linked to the development of proteinuria and the progression of disease in patients with diabetic nephropathy (DN). However, it has been recognized that measurement of podocyte number by light microscope is quite difficult because of the complexity of both podocyte and glomerular structure, which is not suitable for clinical research. In our research institute, we used WT1 as podocyte marker to evaluate the podocyte lesion.

METHODS

In our experiment, we selected the C-terminal antibody of WT1 to stain the nuclei and the N-terminal antibody of WT1 to stain the cytoplasma of podocytes. Forty patients were enrolled with type 2 diabetes and proven to have DN by renal biopsy analysis. DN patients were classified into three groups based on the degree of proteinuria: microalbuminuria (n=10, 30-300mg/24h), overt proteinuria (n=15, 0.5-3.5g/24h), and heavy proteinuria (n=15, >3.5g/24h).

RESULTS

The results demonstrated that the podocyte number was markedly decreased in patients with DN (30-51% reduction). There was a significant negative correlation between the proteinuria and both podocyte density and number. The cover area density of podocyte cytoplasma in glomerulus was also significantly decreased in all DN patients (39-80% reduction). A significant inverse correlation was observed between the cover area density and the degree of proteinuria. The correlation coefficient (r=-0.85) was much higher than that between proteinuria and podocyte density (r=-0.56) or podocyte number (r=-0.36).

CONCLUSION

In conclusion, podocyte damage occurred in patients with DN, even in the early stage and became more dramatic during the course of proteinuria progression. WT1 staining, using the polyclonal antibody to stain the nuclei and monoclonal antibody to stain the cytoplasma of podocytes together, is a valuable alternative technique in the study of podocyte injury.

Endometrial/ioid Stromal Tumors and Related Neoplasms of the Female Genital Tract

Endometrial/ioid stromal tumors comprise a spectrum of mesenchymal neoplasms, ranging from benign to low-grade malignancy to undifferentiated sarcomas, which occur predominantly in the uterus but may rarely originate at extrauterine sites, most commonly in the ovary. These tumors and their morphologic variants are important to recognize as they often cause diagnostic difficulties. This review focuses on the diagnostic criteria and differential diagnosis, including the role of immunohistochemistry.

Immunohistochemical Markers of Value in the Diagnosis of Mesenchymal Lesions of the Female Genital Tract

Pure mesenchymal tumors may occur anywhere in the female genital tract, but they are most common in the uterine corpus, leiomyoma being by far the most prevalent. These tumors, and other uncommon mesenchymal lesions within the uterine corpus and elsewhere in the female genital tract, may result in several diagnostic problems. Morphology remains paramount and, in most cases, an unequivocal diagnosis can be made based on examination of the hematoxylin and eosin stained sections, combined with an appreciation of the clinical and gross pathologic features. In difficult cases, immunohistochemistry can significantly contribute to the final diagnosis. In this article, the immunohistochemistry of neoplastic and nonneoplastic mesenchymal lesions of the female genital tract is discussed site by site, concentrating on markers that are of value in diagnosis and in differential diagnosis. The immunophenotype of mixed epithelial and mesenchymal neoplasms and pure epithelial neoplasms with a component of spindle cells is discussed, where appropriate, because these can enter into the differential diagnosis of a pure mesenchymal lesion.

A new morphological variant of uterine PEComas with sex-cord-like pattern and WT1 expression: more doubts about the existence of uterine PEComas

PEComas are rare neoplasms that are sometimes associated with the tuberous sclerosis complex. They typically contain perivascular epithelioid cells that coexpress muscle and melanocytic markers. However, apart from these classical features, considerable clinical, pathologic, and immunohistochemical variation has been reported. WT1, the Wilms tumor gene product, can be expressed in various tumors from different anatomical sites, including sex-cord and other ovarian tumors with a sertoliform pattern. Neither a sex-cord-like pattern nor WT1 expression has been described in PEComas. Here, we describe a case of uterine PEComa with a pattern of infiltration into the myometrium that is similar to stromal sarcomas, characterized by tongues and endovascular growing. The architecture and cellular morphology were similar to sex-cord tumors, and the PEComa was diffusely and strongly positive for WT1. We reviewed, from our files, an additional 9 cases of PEComa from different sites, and found WT1 expression in one more soft tissue tumor. We discuss the relationship between PEComas and other uterine sarcomas.

Calretinin: diagnostic utility in the female genital tract

The utility of calretinin was first described in the diagnosis of mesothelioma. In the female genital tract, calretinin was initially reported in Wolffian remnants and related lesions and later used in the diagnosis of sex cord stromal tumors of the ovary, endometrial stromal tumors with sex cord-like differentiation, and uterine tumors resembling sex cord tumors of the ovary. This review discusses calretinin expression in normal tissues of the female genital tract and highlights its potential utility in the diagnosis of these subsets of neoplasms with emphasis to tumors that may constitute a problem in their differential diagnosis. In particular, the limited utility of calretinin in the diagnosis of sex cord stromal tumors of the ovary, in the differential diagnosis between mesothelioma and serous tumors involving the ovary and/or peritoneum, and in the differential diagnosis between Wolffian lesions and endometrial carcinoma are addressed.

Cytoplasmic overexpression of WT-1 in gastrointestinal stromal tumor and other soft tissue tumors

The Wilms tumor 1 (WT-1) is a zinc finger transcription factor essential for the development of the kidneys and gonads. Alterations in the WT-1 gene were observed in several tumor types. Depending on the tumor types, WT-1 might function as a tumor suppressor or as a survival factor. WT-1 immunoreactivity in gastrointestinal stromal tumor (GIST) was currently not known. We, therefore, investigated the expression of WT-1 in GIST in comparison to other soft tissue tumors by immunohistochemistry and Western blot analysis. We found that all 28 cases (100%) of GIST are positive for WT-1, diffusely (>75%, 3+) in 13 (46.4%) cases, moderately (26% to 75%, 2+) in 13 (46.4%) cases, and focally (5% to 25%, 1+) in 2 (7.2%) cases. The staining intensity is usually strong. The staining pattern is predominantly cytoplasmic with rare scattered nuclear staining. Similar but less extensive cytoplasmic WT-1 immunoreactivity was detected in 16 of 25 (64%) uterine leiomyosarcoma and 14 of 24 (58.3%) soft tissue leiomyosarcoma. Rare scattered nuclear staining was also seen in uterine leiomyosarcoma and soft tissue leiomyosarcoma, which showed positive cytoplasmic WT-1 reactivity. Only 1 of the 10 solitary fibrous tumors showed weak cytoplasmic WT-1 positivity (10%). No WT-1 staining was detected in 6 cases of fibromatosis. The significance of cytoplasmic expression of WT-1 in GIST and some smooth muscle tumors is unclear and warrant further investigation. The potential roles of WT-1 in the diagnosis and treatment of GIST were discussed.

Mullerian adenosarcomas: an immunophenotypic analysis of 35 cases

Mullerian adenosarcomas (MAs) are rare mixed mesenchymal and epithelial neoplasms that occur most commonly in the uterus. Although the epithelial component is typically benign, the mesenchymal component of most adenosarcomas morphologically resembles that observed in endometrial stromal tumors and is responsible for their clinical behavior. Thus, the differential diagnosis usually includes not only low-grade endometrial stromal tumors, but also adenofibroma, carcinosarcoma, and embryonal rhabdomyosarcoma especially in small samples. The objective of this study was to ascertain the immunophenotypic profile of the epithelial and mesenchymal components of MAs and delineate possible differences between conventional mesenchymal areas and areas of sarcomatous overgrowth. Representative sections from 35 MAs, 28 of them without sarcomatous overgrowth (MA-NSO) and 7 with sarcomatous overgrowth (MA-SO), were included in the study. Thirty tumors arose in the uterus, 4 were pelvic, and 1 originated in the colon. Adequate blocks were selected and immunostained for estrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR), CD10, WT1, smooth muscle actin, desmin, AE1/3 cytokeratin, CD34, calretinin, inhibin, c-kit, and Ki-67. The mesenchymal component expressed ER in 21/27 MA-NSOs but in only 1/7 MA-SOs (65% overall). PR was expressed in 21/26 MA-NSOs and 4/7 MA-SOs (76% overall), whereas AR was positive in 10/27 MA-NSOs and 5/7 MA-SOs (35% overall). CD10 was expressed in 23/28 MA-NSOs but in only 2/7 MA-SOs (71% overall), and WT1 positivity was seen in 22/27 MA-NSOs and 6/7 MA-SOs (79% overall). Sixty-seven percent of MAs expressed smooth muscle actin, 32% desmin, including both examples of MA-SOs with rhabdomyoblastic differentiation, and 25% expressed AE1/3 cytokeratin. CD34 expression was found in 35% of the tumors, but it was almost always patchy in distribution and weak in intensity, as was calretinin expression, seen only in 12% of the cases. Expression of c-kit and inhibin in greater than 5% of the tumor cells was not encountered. The median and mean Ki-67 labeling indices were 10% and 12%, respectively (range, <5% to 40%). The median and mean Ki-67 indices were both 5% in MA-NSOs compared with 30% and 28%, respectively, in MA-SOs. The epithelial compartment demonstrated expression for ER (24/32), PR (23/31), and AE1/3 cytokeratin (33/33); rare cases expressed CD10 (4 cases) and AR (1 case). In summary, the immunophenotype of most MAs resembled that of endometrial stromal tumors (positive for ER, PR, WT1, and CD10, with variable expression of muscle markers, AR and cytokeratin). The proliferative rate in the stromal component was strongly related to the presence of sarcomatous overgrowth. ER, PR, and CD10 expression was lost in MA-SOs relative to conventional low-grade stromal areas of mullerian/mesodermal adenosarcomas, reflecting the "dedifferentiation" of this component.

Immunohistochemical profiling of cytokeratin expression by endometrial stroma sarcoma

Endometrial stromal sarcomas can be confused with several neoplasms because of their inconsistent and widely varied morphologic appearance and frequent immunohistochemical expression of a variety of antigens including cytokeratin. The resulting diagnostic challenge becomes problematic particularly in the diagnosis of metastases resulting from such tumors. Because of the sometime epithelioid appearance of the tumor cells and their expression of cytokeratin, the metastases may be misdiagnosed as poorly differentiated carcinoma. We therefore studied the profile of cytokeratin proteins expression in 17 cases of endometrial stromal sarcomas using a panel of antibodies including cytokeratin cocktail antibody (AE1/AE 3), CK5/6, CK7, CK14, CK16, Cam5.2 (CK8), CK19, CK20, and 34Ebeta12 (CK1, 5, 10, and 14). Of the 17 cases, 8 (47%) stained positive with the cytokeratin cocktail antibody (AE1/AE 3). Of the 8 cases with cytokeratin expression, 5 (63%) stained positive with CK19, and 3 of them stained positive with Cam5.2. The 3 cases that stained positive with Cam5.2 also expressed CK19. Of the 5 cases with CK19, 1 was focally positive for CK5/6, CK7, and 34Ebeta12. None of the cases expressed CK14, CK16, or CK20. These results show that CK19 is most commonly expressed cytokeratin in endometrial stromal tumors. Hence, the inclusion of CK19 in the panel of immunostains may help resolve the diagnostic confusion created by keratin expression in endometrial stromal sarcoma and may also help in the correct diagnosis of endometrial stromal sarcoma at extrauterine sites.

Expression of CD56 and WT1 in ovarian stroma and ovarian stromal tumors

The immunophenotype of ovarian stroma and spindle cell tumors derived from ovarian stroma has not been well studied. We studied the expression of CD56, WT1, estrogen receptor-beta (ER-beta), progesterone receptor (PR), smooth muscle actin, S-100, CD34, and muscle specific actin in 16 normal ovaries, 17 ovarian fibromas, 11 ovarian cellular fibromas, 10 ovarian fibrothecomas, and 11 ovarian leiomyomas. In addition, we studied CD56 and WT1 expression in 7 cases of normal endometrium, 8 uterine smooth muscle tumors, 5 endometrial stromal tumors and 64 nongynecologic (GYN) spindle cell sarcomas. All normal ovaries, ovarian fibromas, fibrothecomas, and ovarian leiomyomas were positive for CD56 and WT1. Most of the normal ovaries, ovarian fibromas, ovarian fibrothecomas, and ovarian leiomyomata also expressed ER-beta and PR. Eight of 17 ovarian fibromas, 5 of 11 ovarian cellular fibromas, and 4 of 10 ovarian fibrothecoma with focal fibroblastic differentiation were positive for smooth muscle actin. A few cases of these tumors also expressed S-100 and CD34. Only rare cases of non-GYN spindle cell sarcomas expressed WT1. Our study results show that ovarian fibromas, fibrothecomas, and leiomyomas have a similar immunophenotype (positive for CD56, WT1, ER-beta, and PR) to that of ovarian stromal cells, supporting an ovarian stromal origin for these neoplasms. However, unlike normal ovarian stromal cells, ovarian fibromas, fibrothecomas, and leiomyomas can also show fibroblastic, smooth muscle, Schwannian, and solitary fibrous tumorlike differentiation. WT1 is a fairly specific marker for spindle cell tumors of gynecologic organs, including ovarian spindle cell tumors, endometrial stromal tumors, and uterine smooth muscle tumors. Non-GYN spindle cell sarcomas rarely express WT1. CD56 is strongly expressed in ovarian stromal cells but not in endometrial stromal cells. CD56 is often expressed by a wide variety of spindle cell sarcomas, thus, it has no value in differentiating GYN from non-GYN spindle cell tumors.

Diagnostic value of WT1 in neuroepithelial tumours

AIMS

Currently, clinical trials using WT1 (Wilms tumour gene) peptide vaccines are conducted in haematopoietic malignancies and solid cancers. Single reports showed that the Wilms tumour gene product WT1 is also expressed in astrocytic neoplasms. Our aim was to investigate WT1 expression in a large cohort of various neuroepithelial tumours of different World Health Organization (WHO) grades and in normal central nervous system (CNS) tissue specimens to test its potential value as a diagnostic marker.

METHODS

Specimens were assessed by RT-PCR, Western blotting and immunohistochemistry. The samples investigated in our study consisted of 334 human neuroepithelial tumours, among those 33 oligodendrogliomas, 219 astrocytomas (including 105 glioblastomas) and 47 ependymomas.

RESULTS

Our results showed a de novo WT1 expression in neuroepithelial tumours. In diffuse astrocytomas and ependymomas, WT1 expression increased significantly with the grade of malignancy. In contrast, no significant difference was seen between WHO grade-II and -III oligodendrogliomas. Controlling for WHO grade, the comparison of oligodendrogliomas with ependymal and astrocytic tumours showed higher expression values for the latter.

CONCLUSIONS

Our study shows that WT1 is expressed de novo in numerous neuroepithelial tumours and increases with the grade of malignancy. These results suggest an important role of WT1 in tumourigenesis and progression in human brain tumours.

Application of immunohistochemistry to gynecologic pathology

CONTEXT

A large variety of tumors and lesions arise in the female genital tract. Although the majority of these can be correctly recognized on routine hematoxylin-eosin-stained slides, occasional cases present a diagnostic challenge. Immunohistochemical stains are extremely useful in resolving many of these problematic cases. As the knowledge in this area is constantly expanding, it is useful to have this updated information in a review form for easy access.

OBJECTIVE

To present our current knowledge of immunohistochemistry of the lesions of the female genital tract in a readily accessible form.

DATA SOURCES

The review is based on previously published articles on this topic.

CONCLUSIONS

Immunohistochemical stains help in reaching a conclusive diagnosis in a variety of problematic lesions seen in gynecologic pathology. As in any other system, immunohistochemical findings need to be interpreted in light of the clinical history and morphologic findings.

Presence of malignant mesothelial cells in the sputum

Malignant pleural mesothelioma and peripheral adenocarcinoma, of the lung, also known as pseudomesotheliomatous adenocarcinoma, have similar clinical and radiological characteristics and even similar microscopic findings, and this makes it difficult to differentiate them. Malignant pleural mesothelioma rarely invades the bronchial lamina or bronchioloalveolar spaces, and tumor cells are not usually found in the sputum. Therefore, the appearance of tumor cells in sputum more likely supports the diagnosis of peripheral lung cancer. We report a rare case in which malignant pleural mesothelioma cells were found in the sputum. For the differential diagnosis of a mass involving both the pleura and lung, physicians should consider that malignant mesothelial cells can be found in the sputum, although this is very rare.

Diagnostic Utility of WT1 Immunostaining in Ovarian Sertoli Cell Tumor

WT1, the Wilms tumor gene product, can be expressed in various tumors from different anatomic sites, including some types of ovarian tumors. Regarding the latter, most studies have focused on surface epithelial-stromal tumors in which serous carcinomas are usually positive and endometrioid carcinomas are negative. Very few studies have specifically investigated this marker in ovarian sex cord-stromal tumors; however, limited data in the literature suggest that WT1 may be frequently expressed in sex cord-stromal tumors. As pure Sertoli cell tumor can be in the histologic differential diagnosis of endometrioid tumors (particularly borderline tumor and carcinoma) and carcinoid, immunostaining for WT1 might be of diagnostic value. Immunohistochemical staining for WT1 was performed in 108 ovarian tumors: pure Sertoli cell tumor (n=26), endometrioid borderline tumor (n=25), classic well-differentiated endometrioid carcinoma (n=23), sertoliform endometrioid carcinoma (n=12), and carcinoid (n=22). Additionally, inhibin and calretinin immunostaining were performed in all cases of Sertoli cell tumor for purposes of comparing expression with WT1. Extent of immunostaining was scored on a 0 to 4+ semiquantitative scale, and immunohistochemical composite scores based on a combination of extent and intensity of immunostaining were calculated in positive cases (possible range, 1 to 12). Nuclear expression of WT1 was present in 96% of Sertoli cell tumors, 16% of endometrioid borderline tumors, 13% of classic well-differentiated endometrioid carcinomas, 25% of sertoliform endometrioid carcinomas, and 0% of carcinoids. In Sertoli cell tumors, expression was diffuse (>50% of positive cells) in all positive cases. When positive in the non-Sertoli cell tumors, the extent of expression tended to be focal to patchy (50% or less positive cells). In Sertoli cell tumors, inhibin and calretinin were expressed in 96% and 54% of cases, respectively. The extent of expression of inhibin tended to be diffuse, similar to WT1; however, the extent of immunostaining for calretinin tended to be focal to patchy. The immunohistochemical composite scores for WT1, inhibin, and calretinin were 11.2, 7.6, and 4.8, respectively. Coordinate patterns for the extent of expression of WT1, inhibin, and calretinin in pure Sertoli cell tumor showed that all 3 markers were positive in 54% of cases; however, 42% were positive for WT1 and inhibin but negative for calretinin. In cases positive for both WT1 and inhibin, expression of both markers was diffuse in 84% of cases, but WT1 was diffuse while inhibin was focal to patchy in 16% of cases. We conclude that ovarian Sertoli cell tumor should be added to the growing list of WT1-positive tumors. This marker is useful for the distinction of Sertoli cell tumor from endometrioid tumors and carcinoid. The diagnostic utility of WT1 in Sertoli cell tumor is similar to inhibin but better than that of calretinin.

Upregulation of Wilms’ tumour gene 1 (WT1) in uterine sarcomas

AIM

Overexpression of Wilms' tumour gene (WT1) has been proven in several tumours. Previous research of our group on the cell cycle of uterine leiomyosarcoma (LMS) and carcinosarcoma (CS) suggested a possible role for WT1. We therefore intended to further explore the expression pattern of WT1 in uterine sarcomas.

METHODS

27 CS, 38 LMS, 15 endometrial stromal sarcomas (ESS) and seven undifferentiated sarcomas (US) were collected. WT1 expression was evaluated by immunohistochemistry (IHC) in 87 samples, by RT-PCR (m-RNA expression) in 23 random selected samples and by Western blotting in 12 samples, separating cytoplasmic and nuclear proteins. A pilot study to detect mutations (exons 7-10) was performed on eight samples.

RESULTS

IHC showed WT1 positivity in 12/27 CS, 29/38 LMS, 7/15 ESS and 4/7 US. All-but-one sample had a positive RT-PCR. All Western blottings were positive with more cytoplasmic expression in 9/12 cases. No mutations were found.

CONCLUSIONS

WT1 is overexpressed in uterine sarcomas. Since increased levels of mRNA determine the biological role, WT1 might contribute to uterine sarcoma tumour biology.

Immunoprofile of Endocervical and Endometrial Stromal Cells and Its Potential Application in Localization of Tumor Involvement

To evaluate and compare the immunophenotype of endocervical and endometrial stromal cells and to asses its potential application in tumor localization. Paraffin sections of benign endocervix (n = 24), benign endometrium (n = 33), endocervical adenocarcinoma (n = 9), endometrial carcinoma (n = 13), and endometrial hyperplasia (n = 16) were stained with antibodies to CD10, Wilms Tumor-1, CD34, smooth muscle actin, and factor XIIIa by immunohistochemistry. In 16 cases, lower uterine segment was also available. Immunoreactivity of stromal cells was recorded as positive (>/=50% staining), focally positive (>/=5%-<50%) or negative (<5%). Endocervical stromal cells (ECSC) in either benign or malignant cervical epithelial lesions were predominantly CD34/CD10 (CD34 dominant immunophenotype). Endometrial stromal cells (EMSCs) in either benign or malignant epithelial lesions were primarily CD34/CD10 (CD10 dominant immunophenotype). Expression of Wilms Tumor-1 was decreased in EMSC of the EMCA when compared to their counterpart in endometrial hyperplasia. There was no differential expression of smooth muscle actin and factor XIIIa identified between ECSC and EMSC. The immunophenotypes of the ECSC and EMSC overlapped in the lower uterine segment. The functional status of the endometrium had no effect on the immunoprofile. The pattern of CD34 and CD10 immunostaining in stromal cells might be helpful in determining tumor involvement in uterine and cervical sites.

Uterine tumour resembling ovarian sex cord tumour is an immunohistochemically polyphenotypic neoplasm which exhibits coexpression of epithelial, myoid and sex cord markers

AIMS

To describe the clinicopathological and immunohistochemical findings in four cases of uterine tumour resembling ovarian sex cord tumour (UTROSCT).

METHODS

Four UTROSCTs were stained with a wide range of antibodies, including epithelial (AE1/3, epithelial membrane antigen), myoid (desmin, alpha smooth muscle actin, h-caldesmon), sex cord (alpha inhibin, calretinin, melan A, CD99) and neuroendocrine (chromogranin, CD56) markers as well as hormone receptors (oestrogen receptor, progesterone receptor, androgen receptor), vimentin, CD10, WT1 and HMB45.

RESULTS

The tumours ranged from 0.8 to 19.5 cm. Three were relatively well circumscribed intramural myometrial lesions; the other was a pedunculated mass attached to the uterine serosa. The tumours were variably composed of solid, corded, trabecular, nested, glandular and retiform arrangements of tumour cells. In three cases, cells with eccentric nuclei and abundant eosinophilic cytoplasm, resulting in a rhabdoid appearance, were a prominent feature. Three cases were diffusely positive with AE1/3 and all with epithelial membrane antigen. Positivity with myoid markers was common with 3, 4 and 1 case respectively staining with desmin, alpha smooth muscle actin and h-caldesmon; 2, 4, 1 and 2 cases respectively were positive with alpha inhibin, calretinin, melan A and CD99. All were chromogranin negative and exhibited diffuse strong staining with CD56. All were diffusely positive with oestrogen receptor, progesterone receptor, vimentin and WT1. Three cases were androgen receptor positive and all were CD10 and HMB45 negative.

CONCLUSIONS

UTROSCT exhibits a polyphenotypic immunophenotype with coexpression of markers of epithelial, myoid and sex cord lineage as well as hormone receptors.

Immunohistochemical and functional biomarkers of value in female genital tract lesions

There has been a marked expansion in the literature pertaining to the use of immunohistochemical markers in female genital tract pathology, especially with regard to diagnosis. This review provides a survey of the antibodies commonly used in the diagnosis of gynecological lesions grouped as to function or type. Prognostic or predictive markers are also discussed where appropriate, although few of these are of value in everyday practice. It is stressed that when immunohistochemistry is used diagnostically, panels of markers provide better information than reliance on a single antibody.

Immunohistochemistry as a diagnostic aid in the evaluation of ovarian tumors

Aspects of immunohistochemistry (IHC), which are useful in the diagnosis of ovarian tumors (mostly neoplasms but also a few tumor-like lesions), are discussed. The topic is first approached by considering the different growth patterns and cell types that may be encountered. Then a few other specific situations in which IHC may assist are reviewed. Selected findings largely, or only, of academic interest are also mentioned. One of the most common situations in which IHC may aid is in the evaluation of tumors with follicles or other patterns which bring a sex cord-stromal tumor into the differential. The distinction between a sex cord tumor and an endometrioid carcinoma with sex-cord-like patterns may be greatly aided by the triad of epithelial membrane antigen (EMA), inhibin, and calretinin, the latter two being typically positive and EMA negative in sex cord tumors, the converse being typical of endometrioid carcinoma. It should be emphasized that granulosa cell tumors may be inhibin negative and, albeit less specific, calretinin is more reliable in evaluating this particular issue. Lack of staining for inhibin and calretinin may also be supportive in leading to consideration of diverse other neoplasms that may form follicles, including metastatic tumors as varied as carcinoid and melanoma. The well-known staining of the latter neoplasm for S-100 protein and HMB-45 may be very helpful in evaluating melanomas with follicular or other unusual patterns, a challenging aspect of ovarian tumor interpretation. The most common monodermal teratoma, struma ovarii, usually has an overt follicular pattern and is easily recognized, but recognition of unusual appearances ranging from oxyphilic to clear cell to various patterns of malignant struma may be greatly aided by a thyroglobulin or TTF 1 stain. IHC for neuroendocrine markers may assist in the diagnosis of primary and metastatic carcinoid tumor. The broad differential diagnosis of glandular neoplasms with an endometrioid-pseudoendometrioid morphology, or mucinous cell type, has been the subject of much exploration in recent years, particularly the distinction between primary and metastatic neoplasms. The well-known CK7 positive, CK20 negative phenotype of primary endometrioid carcinoma, and the converse profile in most metastatic large intestinal adenocarcinomas with a pseudoendometrioid morphology, has been much publicized but albeit an appropriate supportive adjunct in many cases, exceptions from the typical staining pattern may be encountered. It is even less helpful in the case of primary versus metastatic mucinous neoplasia. Evaluation of the expression of mucin gene products has shown mixed, essentially unreliable, results. Experience with other new markers, such as CDX-2, villin, beta catenin, and P504S (racemase), is limited but is in aggregate promising with regard to providing some aid in this area. The rare differential of metastatic cervical adenocarcinoma versus primary ovarian mucinous or endometrioid carcinoma may be aided by strong p16 staining of the former. Staining for alpha-fetoprotein may aid in confirming the diagnosis of endometrioid-like (and hepatoid) variants of yolk sac tumor. Ependymoma of the ovary may also have an endometrioid-like glandular pattern, but positive stains for glial fibrillary acidic protein contrast with the negative results in others neoplasms with a similar pattern. Immunostains may be very helpful in the evaluation of oxyphilic tumors and tumor-like lesions and in some unusual forms of clear cell neoplasia, such as clear cell struma, both subjects being reviewed herein. Immunostains may highlight both the presence and extent of epithelial cells in a variety of circumstances, including microinvasive foci in cases of serous borderline tumors and mucinous carcinomas, and in determining the extent of carcinoma cells and reactive cells within mural nodules of mucinous neoplasms. As in tumor pathology in general, various markers may be crucial in the diagnosis of small round cell tumors of the ovary, and familiar markers of epithelial, lymphoid, leukemic, and melanocytic neoplasms may assist in the analysis of high grade tumors with a poorly differentiated carcinoma, lymphoma-granulocytic sarcoma, malignant melanoma differential. The evaluation of ovarian cystic lesions may be aided by thyroglobulin or TTF 1 (cystic struma), glial fibrillary acid protein (ependymal cysts), and inhibin-calretinin (follicle cysts and unilocular granulosa cell tumors). Stains for trophoblast markers may occasionally aid in the evaluation of germ cell tumors, although routine stains should usually suffice; they may be of academic interest in confirming trophoblastic differentiation in some high grade surface epithelial carcinomas.