IDH-mutant astrocytoma grade 4 was defined as a diffusely infiltrative astrocytic glioma with an IDH1 or IDH2 mutation that exhibited microvascular proliferation or necrosis, CDKN2A/B homozygous deletion, or any combination of these features [3]. The gene discussed is CDKN2A; the disease is astrocytoma (excluding glioblastoma).