Riobello C, López-Hernández A, Cabal VN, et al. - Researchers sought to ascertain if IDH2 and IDH1 mutations may be specific to a subset of undifferentiated and poorly differentiated sinonasal carcinomas. Via sequencing and mutant-specific immunohistochemistry, they analyzed a total of 125 tumor samples of 7 different histologic subtypes for IDH mutations, and the results were then correlated to clinical and follow-up data. Sinonasal undifferentiated carcinoma exhibited the highest incidence of IDH2 mutations, with 11/36 (31%) cases affected. A number of false-negative results were produced with immunohistochemical analysis of mutant IDH1/2, but there was also 1 false-positive tumor. IDH2-mutant vs wild-type cases exhibited more favorable disease-specific survival. A per the data, IDH-mutant sinonasal cancers, irrespective of their histologic subtype, may represent a distinct tumor entity with less aggressive clinical behavior. Clinically, specific IDH-guided therapies may benefit patients with these mutations.