CDKN2A and glioblastoma: Using these, they stratified IDH-mutant glioblastomas into 3 prognostically relevant molecular subgroups: M1 with chromosome 14q loss and either CDK4 amplification or CDKN2A deletion; M2 with either CDK4 amplification, CDKN2A deletion, or chromosome 14q loss; and M3 with no 14q loss, CDK amplification, or CDKN2A deletion.