Differential SALL4 immunoexpression in malignant rhabdoid tumours and epithelioid sarcomas

SALL4 and C-kit positive malignant extrarenal rhabdoid tumor of the pelvis in a child: A diagnostic and therapeutic challenge

ABSTRACT

Extrarenal rhabdoid tumors (ERRTs) are highly aggressive pediatric tumors with very few cases reported in the literature. These tumors, similar to their renal counterparts, are characterized by inactivating mutations of the SMARCB1/INI-1 gene, a member of the SWI/SNF chromatin remodeling pathway. Diagnosis of ERRTs appears challenging owing to its rarity, varied morphological profile with a higher tendency for rhabdoid differentiation, and overlapping features with other SMARCB-1 deficient tumors. Here, we report a case of ERRT in the pelvis of a three-year-old child with an unusual expression of SALL4 and C-kit on immunohistochemistry. A complete immunohistochemical workup might help in differentiating ERRTs from other SMARCB1/INI1-deficient soft tissue tumors. The expression of stem cell markers in the presented case also suggests that these tumors might originate from or share similarities with embryonic stem cells or germ cells.

Decoding the rhabdoid riddle in liver: A rare case of primary hepatic malignant rhabdoid tumor with a comprehensive literature review

Malignant rhabdoid tumor of the liver is a rare, highly aggressive primary hepatic malignancy occurring primarily in infants. Establishing a definitive diagnosis is challenging due to its rarity, non-specific clinicoradiologic findings, and overlapping morphologic features. Herein, we present the cytomorphologic and immunocytochemical characteristics of a rare case of primary hepatic Malignant rhabdoid tumor (MRT) in an infant. A 5-month-old female child presented with progressively increasing firm mass in the upper abdomen, progressive pallor, sudden onset respiratory distress, and difficulty feeding. On examination, the child had massive, firm nodular hepatomegaly. Ultrasonography of the abdomen revealed a heterogeneously hypoechoic lesion in the left lobe of the liver. Serum alpha-fetoprotein levels were within normal limits. An ultrasound-guided fine-needle aspiration cytology (FNAC) from the liver mass showed predominantly dispersed large, markedly pleomorphic tumor cells with round to oval eccentrically placed nuclei, prominent nucleoli, and moderate cytoplasm. On immunocytochemistry, tumor cells showed positivity for vimentin, cytokeratin, and EMA and demonstrated a loss of INI1, confirming the diagnosis of MRT. The index report highlights the distinctive clinicopathological features of a hepatic malignant rhabdoid tumor along with the key differential diagnoses, which may pose a diagnostic conundrum. A high index of clinical suspicion and a thorough understanding of its cytomorphological and immunochemical characteristics are crucial for an accurate diagnosis.

NUT carcinoma and thoracic SMARCA4-deficient undifferentiated tumour: facts and controversies

NUT carcinoma and thoracic SMARCA4-deficient undifferentiated tumour are unique entities in the 5th edition of the World Health Organisation (WHO) Classification of Thoracic Tumours, whose definitions include molecular genetic abnormalities. These aggressive tumours require rapid work-ups on biopsies, but a broad list of differential diagnoses poses challenges for practising pathologists. This review provides an update on their key clinicopathological and molecular characteristics, as well as controversies regarding tumour classification and diagnostic strategy. Phenotypical assessment plays a substantial role in diagnosis because recurrent and predictable clinicopathological findings exist, including robust immunohistochemical phenotypes. Accurate diagnosis is crucial for appropriate management and a clearer understanding of the disease.

Malignant rhabdoid tumour of liver: Conundrum on ascitic fluid

Ascitic fluid analysis is an important tool for diagnosis and staging. Cytological analysis is routinely done as a part of workup for ascites. This is challenging in paediatric malignancies where multiple differentials need to be considered at times with limited cellularity. We present a case of malignant rhabdoid tumour of liver in a young child presenting with abdominal lump and ascites. The diagnosis was offered on ascitic fluid cytology based on cytomorphology, supporting immunohistochemistry and later confirmed on biopsy. This report briefly discusses its differentials and approach to diagnosis.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

Epithelioid Vascular Lesions: The Differential Diagnosis and Approach in Cytology and Small Biopsies

Vascular neoplasms are rare tumors with a multitude of clinical presentations and behavior, which make accurate identification and subclassification challenging on limited small biopsies. Within the spectrum of these lesions, the ones with epithelioid morphology, such as epithelioid hemangioendothelioma and epithelioid angiosarcoma, are particularly challenging given the morphologic overlap with nonvascular lesions and the limited cells due to hemodilution on sampling. Herein, we review the differential diagnosis of epithelioid vascular neoplasms, with a focus on the cytomorphology, differential diagnoses, and ancillary studies that pathologists should be aware of when evaluating small biopsies and aspirates, including novel translocations, and associated monoclonal immunohistochemistry antibodies, that can help in the diagnosis of some of these tumors. Awareness of these morphologic and ancillary study findings in these rare tumors will hopefully allow pathologists to recognize and render-specific diagnoses on limited samples of these challenging lesions.

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

AIMS

SMARCB1 (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 RESULTS

Ten 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.

CONCLUSION

Our 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.

Primary adult sellar SMARCB1/INI1-deficient tumor represents a subtype of atypical teratoid/rhabdoid tumor

Loss of function in SMARCB1/INI1 has been observed in a group of malignancies collectively defined as SMARCB1/INI1-deficient neoplasms. Primary intracranial SMARCB1/INI1-deficient tumors in adults are extremely rare. We collected eight primary adult sellar SMARCB1/INI1-deficient tumors to study their clinicopathological and (epi)genetic characteristics. We performed a comprehensive assessment of the clinical, radiological, morphological and immunohistochemical features. FISH analysis for the SMARCB1 locus and target exome sequencing for 425 cancer relevant genes were performed. Furthermore, six bona fide proximal epithelioid sarcoma (PES), fourteen atypical teratoid/rhabdoid tumors (ATRT) in brain and five pediatric poorly differentiated chordomas (PDC) in the clivus were collected for comparative analysis of differential diagnostic maker expression and DNA methylation profile. The median age was 47.1 years, ranging from 26 to 73 years. On morphology, tumors were characterized by sheets of monomorphic larger epithelioid-like cells, in two cases with rhabdoid cells. "Stag-horn" vasculatures were observed in five cases. The loss of INI1 protein expression, co-expression of epithelial makers and mesenchymal markers were observed in all cases. CD34 expression was observed in six cases. Heterozygous deletion of SMARCB1/INI1 was confirmed using FISH in six cases. The results of target exome sequencing showed three patients harbored heterozygous point mutations in SMARCB1. The epigenetic features of the primary adult sellar SMARCB1/INI1-deficient tumors resembled the ATRT-MYC subgroup, but clustered apart from PES and PDC. Based on epigenetic characteristics, primary adult sellar SMARCB1/INI1-deficient tumors represent a subtype of ATRT with similar epigenetic characteristics of ATRT-MYC subgroup. Our findings suggest that DNA methylation profiling should be utilized for differential diagnosis for the majority of epithelioid sarcoma and (sellar) rhabdoid tumor.

Poorly differentiated chordoma showing loss of SMARCB1/INI1: Clinicopathological and radiological spectrum of nine cases, including uncommon features of a relatively under-recognized entity

Poorly differentiated chordoma is a newly recognized entity in the recent World Health Organization (WHO) classification of tumors of soft tissue and bone. Slightly over 60 such cases have been documented. Herein, we present a clinicopathological profile, including radiological features, of nine cases, which occurred in five males and four females, with age varying from 1 to 29 years (median = 43), in the cervical spine (n = 2), skull base (n = 2), clivus (n = 2), thoracic spine (n = 1) lumbar spine (n = 1) and coccyx (n = 1) Average tumor size was 4.8 cm. None of the 6-referral cases was diagnosed as a poorly differentiated chordoma at the referring laboratory. Histopathologically, all cases displayed a cellular tumor comprising polygonal cells (n = 9) displaying moderate to marked nuclear pleomorphism with prominent nucleoli (n = 7), eosinophilic (n = 9) to vacuolated cytoplasm (n = 7), rhabdoid morphology (n = 4), interspersed mitotic figures (n = 5), focal necrosis (n = 6) and inflammatory cells (n = 9). A single tumor displayed areas resembling classic chordoma, transitioning into poorly differentiated areas. There were multinucleate giant cells and physaliphorous cells in two tumors, each, respectively. Immunohistochemically, tumor cells were positive for AE1/AE3 (7/7), EMA (7/7), cytokeratin (CK) MNF116 (1/1), OSCAR (1/1), brachyury (9/9, diffusely), S100P (4/7, mostly focally), and glypican 3(2/4). SMARCB1/INI1 was completely lost in all nine tumors. A single case tested by FISH showed homozygous deletion of the SMARCB1 gene. Therapeutically (n = 7), all patients were treated with surgical resection (invariably incomplete) (n = 5), followed by adjuvant radiation therapy (n = 4) and chemotherapy (n = 4). While a single patient partially responded to treatment and another patient is alive with no evidence of disease after 23 years, three patients died of disease, six, eight, and 11 months post-diagnosis, despite adjuvant treatments. A single patient presented with a metastatic lung nodule, while another developed widespread metastasis. Poorly differentiated chordomas display a spectrum of features, are associated with a lower index of suspicion for a diagnosis, and display aggressive outcomes. Critical analysis of radiological and histopathological features, including necessary immunostains (brachyury and SMARCB1/INI1), is necessary for their timely diagnosis. These tumors show loss of SMARCB1/INI1 immunostaining and homozygous deletion of INI1/SMARCB1 gene.

SWI/SNF-deficient thoraco-pulmonary neoplasms

The SWI/SNF complexes are major regulators of gene expression and their alterations occur in a large array of cancers both of epithelial and mesenchymal lineages. Malignant rhabdoid tumors were the first malignancies linked to deregulation of these complexes with the involvement of SMARCB1 in their development but genetic alterations affect all subunits in other malignancies. In the chest and lung regions, SMARCA4 (BRG1) is the most frequently altered subunit and is involved in the pathogenesis of two subtypes of tumors, including bona fide carcinomas (SMARCA4-deficient non-small cell lung cancers) but also undifferentiated tumors that harbor an undifferentiated phenotype close to those of malignant rhabdoid tumors (SMARCA4-undifferentiated tumors). Although their histogenesis is yet to be fully understood, these tumors are associated with distinct clinical and pathological features even though some overlapping features have been reported in rare cases. SMARCA4 deficiency is easily asserted by immunohistochemistry that show the loss of nuclear expression of the protein in the nuclei of tumor cells. These tumors are commonly associated with high-grade cytological features, rhabdoid cytomorphology, solid architecture and extensive necrosis. The typical immunohistochemical signature of SMARCA4-UT combines co-inactivation of SMARCA2 (BRM) and the overexpression of SOX2 and SALL4. No specific therapeutic strategies have been so far developed for SMARCA4-deficient neoplasms. SMARCB1 subunit is involved in the development of several SMARCB1-deficient sarcomas on top of malignant rhabdoid tumors that may develop in the thorax. Malignant rhabdoid tumors affect mostly children of less than 5y. The differential diagnosis includes epithelioid sarcomas, malignant myoepithelial tumors or myoepithelial carcinomas, extra-skeletal myxoid chondrosarcomas and synovial sarcomas.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

[Pathological and molecular features of malignancies underlined by BAF complexes inactivation]

BAF complexes are chromatin remodelling complexes made up of 15 subunits which overview transcription regulation. A subset of their subunits are notoriously linked to cancer, with the examples of SMARCB1, SMARCA4, ARID1A/1B and PBRM1. The complexes act as tumor suppressor genes, commonly mutated in a wide array of malignancies with an overrepresentation of sarcomas and tumors of the central nervous system. The recurrent inactivation of their genes points towards their driving role in the tumorigenesis of SMARCB1 in malignant rhabdoid tumors and SMARCA4 in small cell carcinoma of the ovary, hypercalcemic type. These tumors are morphologically similar composed of solid sheets of cells displaying vesicular nuclei dotted with clear chromatin and conspicuous nucleoli. Genomically, they share simple diploid profiles with no other alterations than in the culprit gene. Other mesenchymal tumors, distinct from malignant rhabdoid tumors are associated with BAF alterations, namely epithelioid sarcomas, SMARCA4-deficient thoracic sarcomas. BAF subunits are mostly inactivated through mutations or deletions but also occur through translocations in medullary carcinoma of the kidney and synovial sarcomas. Apart from tumors displaying recurrent alterations of the complexes, some variants or tumor variants display BAF alterations, including epithelioid malignant peripheral nerve sheet tumors and poorly differentiated chordomas. Lastly, some malignancies display low frequency of BAF alterations, in keeping with their passenger role in tumorigenesis with the example of dedifferentiated carcinomas, especially in colon, lung and uterus. BAF complexes alterations correlate with morphological features recognizable by microscopy, paving the way for their routine diagnosis and potential therapeutic prospects.

Embryonic signature distinguishes pediatric and adult rhabdoid tumors from other SMARCB1-deficient cancers

Extra-cranial rhabdoid tumors (RT) are highly aggressive malignancies of infancy, characterized by undifferentiated histological features and loss of SMARCB1 expression. The diagnosis is all the more challenging that other poorly differentiated cancers lose SMARCB1 expression, such as epithelioid sarcomas (ES), renal medullary carcinomas (RMC) or undifferentiated chordomas (UC). Moreover, late cases occurring in adults are now increasingly reported, raising the question of differential diagnoses and emphasizing nosological issues. To address this issue, we have analyzed the expression profiles of a training set of 32 SMARCB1-deficient tumors (SDT), with ascertained diagnosis of RT (n = 16, all < 5 years of age), ES (n = 8, all > 10 years of age), UC (n = 3) and RMC (n = 5). As compared with other SDT, RT are characterized by an embryonic signature, and up-regulation of key-actors of de novo DNA methylation processes. Using this signature, we then analysed the expression profiling of 37 SDT to infer the appropriate diagnosis. Thirteen adult onset tumors showed strong similarity with pediatric RT, in spite of older age; by exome sequencing, these tumors also showed genomic features indistinguishable from pediatric RT. In contrary, 8 tumors were reclassified within carcinoma, ES or UC categories, while the remaining could not be related to any of those entities. Our results demonstrate that embryonic signature is shared by all RT, whatever the age at diagnosis; they also illustrate that many adult-onset SDT of ambiguous histological diagnosis are clearly different from RT. Finally, our study paves the way for the routine use of expression-based signatures to give accurate diagnosis of SDT.

Clinicopathological and molecular characterization of SMARCA4-deficient thoracic sarcomas with comparison to potentially related entities

A growing number of studies suggest critical tumor suppressor roles of the SWI/SNF chromatin remodeling complex in a variety of human cancers. The recent discovery of SMARCA4-deficient thoracic sarcomas has added to the list of tumor groups with the SMARCA4 inactivating mutation. To better characterize these tumors and establish their nosological status, we undertook a clinicopathological and molecular analysis of 12 SMARCA4-deficient thoracic sarcomas and compared them with three potentially related disease entities. Eleven men and one woman with SMARCA4-deficient thoracic sarcomas (aged 27-82 years, median 39 years) were included in the study. Most of the patients had heavy smoking exposure and pulmonary emphysema/bullae. The primary tumors were large and involved the thoracic region in all cases and simultaneously affected the abdominal cavity in 3 cases. The patients followed a rapid course, with a median survival of 7 months. Histologically, all tumors showed diffuse sheets of mildly dyscohesive, relatively monotonous, and undifferentiated epithelioid cells with prominent nucleoli. Immunohistochemically, all tumors demonstrated a complete absence (8 cases) or diffuse severe reduction (4 cases) of SMARCA4 expression. Cytokeratin, CD34, SOX2, SALL4, and p53 were expressed in 6/12, 10/12, 10/12, 10/12, and 7/10 cases, respectively. SMARCA2 expression was deficient in 11/12 cases, and none (0/8) expressed claudin-4. Targeted sequencing was performed in 5 cases and demonstrated the inactivating SMARCA4 mutation in each case and uncovered alterations in TP53 (5/5), NF1 (2/5), CDKN2A (2/5), KRAS (1/5), and KEAP1 (1/5), among others. Comparative analysis supported the distinctiveness of SMARCA4-deficient thoracic sarcomas as they were distinguishable from 13 malignant rhabdoid tumors, 15 epithelioid sarcomas, and 12 SMARCA4-deficient lung carcinomas based on clinicopathological and immunohistochemical grounds. SMARCA4-deficient thoracic sarcomas constitute a unique, highly lethal entity that requires full recognition and differentiation from other epithelioid malignancies involving the thoracic region.

Reclassification of rhabdoid tumor and pediatric undifferentiated/unclassified sarcoma with complete loss of SMARCB1/INI1 protein expression: three subtypes of rhabdoid tumor according to their histological features

Rhabdoid tumor is characterized by rhabdoid cells and shows complete loss of SMARCB1/INI1 protein expression. In existing classifications, the diagnostic synonyms vary depending on the anatomic site: rhabdoid tumors in the central nervous system or extra-central nervous system are, respectively, classified as atypical teratoid/rhabdoid tumor or malignant rhabdoid tumor. In this study, we analyzed the histological, immunohistochemical, microRNA, and clinicopathological statuses of tumors initially diagnosed as malignant rhabdoid tumor (n=33), atypical teratoid/rhabdoid tumor (n=11), and pediatric undifferentiated/unclassified sarcoma (n=8) with complete loss of SMARCB1/INI1 expression, and considered the possibility of their histological reclassification. Our analysis indicated that the tumors could be histologically reclassified into three groups: conventional-type tumors resembling malignant rhabdoid tumor, atypical teratoid/rhabdoid-type tumors resembling atypical teratoid/rhabdoid tumor, and small cell-type tumors resembling malignant lymphoma. The reclassified conventional type was composed of 27 malignant rhabdoid tumors and 9 atypical teratoid/rhabdoid tumors (36 cases). The atypical teratoid/rhabdoid type consisted of six malignant rhabdoid tumors, two atypical teratoid/rhabdoid tumors, and two undifferentiated/unclassified sarcomas (10 cases). The six cases of small cell type were made up of six undifferentiated/unclassified sarcomas. All of the available tumor specimens were positive for vimentin and epithelial marker (EMA, CAM5.2, or AE1/AE3). MicroRNA profiles were not significantly different between the conventional- and small cell-type tumors (Pearson's correlation coefficient: 0.888300 or 0.891388). There was no significant difference in overall survival between atypical teratoid/rhabdoid tumor and malignant rhabdoid tumor (P=0.16). In addition, there were no significant differences in survival between any of the reclassified combinations. In conclusion, we could classify eight tumors initially diagnosed as undifferentiated/unclassified sarcomas into two cases of atypical teratoid/rhabdoid type and six cases of small cell type. We suggest that reclassification of malignant rhabdoid tumors into three groups according to their histologic features rather than the traditional classification by sites of origin would be favorable for their histopathological diagnosis.

SALL4, the missing link between stem cells, development and cancer

There is a growing body of evidence supporting that cancer cells share many similarities with embryonic stem cells (ESCs). For example, aggressive cancers and ESCs share a common gene expression signature that includes hundreds of genes. Since ESC genes are not present in most adult tissues, they could be ideal candidate targets for cancer-specific diagnosis and treatment. This is an exciting cancer-targeting model. The major hurdle to test this model is to identify the key factors/pathway(s) within ESCs that are responsible for the cancer phenotype. SALL4 is one of few genes that can establish this link. The first publication of SALL4 is on its mutation in a human inherited disorder with multiple developmental defects. Since then, over 300 papers have been published on various aspects of this gene in stem cells, development, and cancers. This review aims to summarize our current knowledge of SALL4, including a SALL4-based approach to classify and target cancers. Many questions about this important gene still remain unanswered, specifically, on how this gene regulates cell fates at a molecular level. Understanding SALL4's molecular functions will allow development of specific targeted approaches in the future.

Myoepithelioma-like Tumors of the Vulvar Region: A Distinctive Group of SMARCB1-deficient Neoplasms

We describe 9 tumors that resemble soft tissue myoepitheliomas but possess certain traits that do not fit perfectly into this category. These tumors, herein referred to as "myoepithelioma-like tumors of the vulvar region," occurred in the subcutis of the vulva and surrounding regions of adult women aged 24 to 65 years. Histologically, the tumors measured 2 to 7.7 cm and were well circumscribed, focally encapsulated, and lobulated. Tumor cells had an epithelioid to spindled shape, with fine amphophilic cytoplasm, and uniform nuclei with vesicular chromatin and nucleoli. The tumor stroma was relatively hypervascular, and comprised a mixture of myxoid and nonmyxoid components. Myxoid areas accounted for <5% to 95% of the tumor volume, wherein cells proliferated singly or in a loosely cohesive manner. In nonmyxoid areas, tumors cells grew in diffuse sheets or storiform arrangements. Immunohistochemically, all tested tumors were positive for vimentin, epithelial membrane antigen, and estrogen receptor; most tumors expressed actin. All tumors were negative for S100 protein, glial fibrillary acidic protein, and CD34. Cytokeratin expression was absent in all but 2 tumors, which showed rare positivity. SMARCB1 expression was deficient in all cases. EWSR1, FUS, and NR4A3 rearrangements were absent. All tumors were treated through surgery. Although 3 tumors regrew or recurred after intralesional excision, all 9 patients were alive without metastases at a mean follow-up of 66 months. Myoepithelioma-like tumors of the vulvar region constitute a distinct group of tumors, although future research is required to determine whether they are an unusual subtype of soft tissue myoepitheliomas or a separate disease.

Pattern of SMARCB1 (INI1) and SMARCA4 (BRG1) in poorly differentiated endometrioid adenocarcinoma of the uterus: analysis of a series with emphasis on a novel SMARCA4-deficient dedifferentiated rhabdoid variant

The role of the switch/sucrose nonfermenting chromatin remodeling complex in the initiation and progression of cancer is emerging. In the female genital tract, only ovarian small cell carcinoma, hypercalcemic type harbors recurrent inactivating SMARCA4 mutations. Otherwise, only rare case reports documented SMARCB1 involvement in endometrial cancer. We analyzed 24 grade 3 uterine endometrioid adenocarcinomas and 2 undifferentiated carcinomas for immunohistochemical expression of SMARCB1 and SMARCA4. All tumors showed high-grade nuclear features with a predominance of solid growth pattern. All cases showed intact nuclear SMARCB1 expression in all tumor cells. However, 1 case of a 78-year-old woman showed complete loss of SMARCA4 in 90% of the tumor with retained expression in 10% of the tumor. The SMARCA4-intact component was a moderate-to-poorly differentiated endometrioid adenocarcinoma. The SMARCA4-deficient dominating component showed solid growth of highly anaplastic undifferentiated large cells with prominent rhabdoid features. None of the 25 SMARCA4-intact cases showed rhabdoid cell morphology. To our knowledge, this is the first systematic study of SMARCB1 and SMARCA4 expression in endometrioid adenocarcinoma of uterus and the first description of a novel SMARCA4-deficient variant of dedifferentiated/undifferentiated endometrial carcinoma. The presence of a differentiated SMARCA4-intact endometrioid component points to a novel pathway of dedifferentiation in endometrioid adenocarcinoma as a consequence of a "second hit." This case further underlines the close link between the "rhabdoid phenotype" and the SWI/SNF pathway.