IDH1 and oligodendroglioma: CDK4 amplification was found in four cases: two cases of IDH-mutant astrocytomas, a case of IDH-mutant and 1p/19q co-deleted oligodendroglioma, and a case of IDH-wild-type diffuse astrocytic tumor, which ultimately has been reclassified as a grade 4 glioblastoma due to the presence of EGFR amplification.