CDKN2A/B homozygous deletion in IDH-mutant astrocytomas has been shown to be a negative prognostic marker, and they should be diagnosed as astrocytoma IDH-mutant, CNS WHO grade 4 despite lack of microvascular proliferation or necrosis [5, 27]. The gene discussed is IDH1; the disease is astrocytoma (excluding glioblastoma).