The recent 5th edition of the WHO Classification of Head and Neck Tumours includes new entities in which molecular genetics have an important diagnostic role, including HPV-related multiphenotypic sinonasal carcinoma, SWI/SNF-deficient sinonasal carcinoma and adenocarcinoma [1], and a subset of emerging entities including the IDH-mutated malignancies classified in the category of sinonasal undifferentiated carcinoma (SNUC) [1]. The gene discussed is IDH2; the disease is sinonasal undifferentiated carcinoma.