IDH1 and astrocytoma (excluding glioblastoma): Assessed the prognostic utility of CDKN2A HD, CDK4 amplification, and RB1 HD in IDH-mutant astrocytomas. Only CDKN2A HD predicted poor prognosis in univariate and multivariate analyses. It was also suggested that CDKN2A HD could define grade 4 astrocytomas.