Three main entities have emerged in adult diffuse gliomas, based on their mutational spectrum, histological characteristics, copy-number-variations and methylation patterns: (a) GBM, IDH1/2 wild-type (IDHwt), grade IV; (b) astrocytoma, IDH1/2 mutant (IDHmut), grades II–IV; and (c) oligodendroglioma, IDHmut, 1p/19q codeleted, grades II–III [12]. This evidence concerns the gene IDH1 and oligodendroglioma.