For example, oligodendrogliomas are defined by the presence of both isocitrate dehydrogenase (IDH) mutation (either IDH1 or IDH2) and 1p/19q co-deletion irrespective of the morphology of an infiltrating glioma, while adult infiltrating gliomas without 1p/19q co-deletion are separated into IDH-mutant and IDH-wildtype subgroups, the latter in the adult setting now exclusively termed “glioblastoma” [7, 10, 15, 22, 28, 31, 32, 36, 39, 45, 48]. Here, IDH2 is linked to oligodendroglioma.