IDH1 and astrocytoma (excluding glioblastoma): In the 2021 classification, all IDH-mutant diffuse astrocytic tumors with intact 1p/19q chromosomes are considered a single type called astrocytoma, IDH-mutant with WHO grades ranging from 2 to 4. Grading of these tumors takes into account molecular findings such as the homozygous deletion of CDKN2A/B, which is associated with a worse prognosis.