The presence of EGFR amplification, TERT promoter mutation, and/or simultaneous gain of chromosome 7 and loss of chromosome 10 (+ 7/− 10) are currently considered molecular grade 4 features in IDH-wild-type glioblastoma, and homozygous loss of CDKN2A/B is considered a molecular grade 4 feature in IDH-mutant astrocytoma and a grade 3 feature in oligodendroglioma [127], although rare exceptions have been reported [11, 211]. Here, IDH1 is linked to oligodendroglioma.