IDH-mutant astrocytomas are WHO grade 4 in the presence of microvascular proliferation, necrosis, and/or homozygous CDKN2A deletion [15, 65, 90], although other molecular features have been suggested as well [3, 15, 29, 70, 105]. Here, CDKN2A is linked to astrocytoma (excluding glioblastoma).