Unlike SMARCB1 (INI1) loss, which is most often an “entity-defining” event in tumors such as epithelioid sarcoma and pediatric rhabdoid tumors, SMARCA4 loss occurs more often as a late genetic event driving dedifferentiation in carcinomas of various types [15], but also as a rare primary genetic event in histogenetically diverse entities [16, 17]. The gene discussed is SMARCB1; the disease is carcinoma.