Among diffusely infiltrating gliomas, the mutational status of isocitrate dehydrogenase (IDH1 or IDH2 genes) is a fundamental determinant of biologic behavior, which, in combination with additional molecular features, is now a defining criterion of the diagnostic category of IDH-mutant (IDHm) astrocytoma [1]. This evidence concerns the gene IDH2 and astrocytoma (excluding glioblastoma).