The three adult types of diffuse gliomas are represented by the (1) astrocytoma, IDH-mutant (grades 2, 3, and 4); (2) oligodendroglioma, IDH-mutant, and 1p/19q-codeleted (grades 2 and 3) and (3) glioblastoma, IDH-wildtype (grade 4) (1). This evidence concerns the gene IDH1 and oligodendroglioma.