The 2021 WHO classification of CNS tumors combines histological and molecular grading, where molecular parameters can override histological findings in assigning a grade, with examples including CDKN2A and/or CDKN2B homozygous deletion in IDH-mutant astrocytoma, as well as TERT promoter mutation, EGFR amplification, and + 7/−10 chromosome copy number changes in IDH-wildtype GBM [1]. The gene discussed is IDH2; the disease is glioblastoma.