Cytopathologic and histopathologic characteristics of SMARCB1 deficient neoplasm and correlation with molecular and immunohistochemical findings.
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INTRODUCTION: SMARCB1 deficient neoplasm is an aggressive and heterogeneous group of neoplasms. The morphology of the neoplasm is highly variable. Recent clinical trials show that targeted therapy with EZH2 inhibitor tazemetostat can improve patients' survival. Thus, it is important to recognize the entity for appropriate clinical management. MATERIAL AND METHODS: The pathology archive was searched over 10-year period for cases with diagnosis of SMARCB1 deficient neoplasm and aberrant expression of SMARCB1 (INI-1). Cyto- and histomorphology, immunohistochemistry (IHC) and molecular findings were characterized. RESULTS: 54 cases with complete loss of SMARCB1 (INI-1) on IHC staining were identified, including 5 serous fluids, 10 fine needle aspirations (FNA), 18 biopsy cores and 21 surgical resections. The median age of patients was 35.8 years, ranging from 14 days to 87 years. The female to male ratio was 1.07:1.00. The most involved anatomic sites in descending order were: head and neck (n = 14), CNS (n = 11), lymph node (n = 8), thorax/lung (n = 6), liver (n = 5) and others (n = 10). In addition to published morphology patterns, characteristic cytomorphology included phenotypic features of poorly differentiated carcinoma with pleomorphic tumor cells, basaloid, rhabdoid or epithelioid sarcomas. These tumors had frequently positive cytokeratin stains. Complex genetic abnormalities were identified, including aberrant SMARCB1/INI-1, PIK3C2B, RAF, MAP3K14, FBXO11 and others. 10 cases of partial loss of SMARCB1 (/INI-1) were also included. CONCLUSIONS: The ancillary testing of SMARCB1 (INI-1) should be considered in a subset of patients whose tumor demonstrates bizarre cytomorphology, especially in poorly differentiated or markedly pleomorphic tumors. The cytological recognition is critical for appropriate management.