CDKN2A and astrocytoma (excluding glioblastoma): Based on these findings, according to the change in the grading of IDH-mutant astrocytomas in the 2021 WHO CNS tumors classification, tumors containing CDKN2A/CDKN2B HD are classified as grade 4 even if they do not contain microvascular proliferation and/or necrosis (1).