Thoracic SMARCA4-deficient undifferentiated tumor

The tumor is comprised of high-grade cells without differentiation (panel A). Some of the cells have eccentrically placed nuclei, imparting a rhabdoid phenotype to them. The diagnosis is established by demonstrating nuclear loss of BRG1 (SMARCA4) on immunohistochemistry (panel B). Normal lymphocytes serve as an internal control (positive).