SMARCB1 and sinonasal undifferentiated carcinoma: In the sinonasal tract, the appearance of NUT carcinoma overlaps with those of other poorly differentiated neoplasms or small round blue cell tumors, including sinonasal undifferentiated carcinoma (SNUC), Ewing sarcoma/primitive neuroectodermal tumors (PNET), Epstein-Barr virus (EBV)-associated lymphoepithelial carcinoma, lymphoma/leukemia, olfactory neuroblastoma, small cell neuroendocrine carcinoma, melanomas, rhabdomyosarcoma and the recently described SMARCB1(INI1)-deficient sinonasal carcinoma (5, 16–19).