SMARCB1 and rhabdoid tumor: Due to the high degree of dedifferentiation observed in SMARCA4-deficient undifferentiated RCC, these tumors are morphologically similar to SMARCB1-deficient malignant rhabdoid tumor (MRT), rhabdomyoblastic RCC, and other small round cell undifferentiated tumors, which can lead to misdiagnosis (10–12).