SWItch/Sucrose Non-Fermentable (SWI/SNF) -related matrix-associated actin-dependent regulator of chromatin (SMARC) subfamily B member 1 (SMARCB1) deficient sinonasal carcinoma (SdSNC) is a rare variant of sinonasal undifferentiated carcinoma (SNUC). The gene discussed is SMARCB1; the disease is nasal cavity and paranasal sinus carcinoma.