PMC8794332_01
Thoracic SMARC4-deficient undifferentiated tumor (SMARCA4-UT). (A) At scanning power the biopsy shows sheets of neoplastic cells (left side) and large areas of necrosis (right side) (H&E). (B) The tumor cells are of epithelioid morphology with round to oval nuclei and prominent nucleoli (H&E). (C) Many of the neoplastic cells show eosinophilic cytoplasm with an eccentric nucleus suggestive of rhabdoid cytology (H&E). Immunohistochemical stains show the following results: (D) The tumor cells are negative for Oscar keratin. (E) They are focally positive for CD30. (F) The neoplastic cells lack expression of BRG1 while benign cells are positive for BRG1 (nuclear stain). (G) Expression of INI-1 is preserved. Magnification: x scan (A), x400 (B,D,E,F,G), x600 (C).
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A needle core biopsy of an 'anterior mediastinal lymph node' shows extensive necrosis with scattered clusters and small sheets of medium-sized atypical epithelioid cells (Figure 1A). The atypical cells are characterized by a moderate amount of cytoplasm (Figure 1B). Some neoplastic cells have rhabdoid features (Figure 1C). Immunostains show that the tumor cells lack expression of multiple keratins including Oscar keratin (Figure 1D), pankeratin, high molecular weight keratin, CK5/6, CK7, and CK20, essentially excluding carcinoma and malignant mesothelioma. The tumor cells are focally positive for CD30 (Figure 1E), and focally weakly for CD138 while they lack staining with p63, TTF 1, napsin, CD31, S100, calretinin, D2-40, WT-1, NUT, SALL-4, myogenin, desmin, and SMA. Therefore, a BRG1 immunostain is performed which shows loss of expression of BRG1 with an intact positive internal control (Figure 1F). INI-1 expression is preserved (Figure 1G).