ARID1A and sinonasal undifferentiated carcinoma: Recently, a new methylation-based classification for sinonasal tumors has been proposed, recognizing four molecular subtypes and sinonasal undifferentiated tumors (SNUC), two of them with NEC-like features (NEC-like IDH2 and NEC-like SMARCA4/ARID1A), a third group characterized by SMARB1 loss and a fourth one with characteristics of adenoid cystic carcinoma [44].