While in the 2016 update IDH-mutant tumors comprised 5 different entities (Diffuse astrocytoma WHO grade II, IDH-mutant; Anaplastic astrocytoma WHO grade III, IDH-mutant; Glioblastoma WHO grade IV, IDH-mutant; Oligodendroglioma WHO grade II, IDH-mutant and 1p/19q-codeleted; Anaplastic oligodendroglioma WHO grade III, IDH-mutant and 1p/19q-codeleted) the novel classification recognizes just two entities, now termed “types”: “Astrocytoma, IDH-mutant” and “oligodendroglioma, IDH-mutant and 1p/19q-codeleted”. This evidence concerns the gene IDH1 and anaplastic oligodendroglioma.