IDH1 and astrocytoma (excluding glioblastoma): Adult HGGs are currently divided into four groups: (1) grade III oligodendroglioma [1p/19 co-deleted, isocitrate dehydrogenase (IDH)-mutant]; (2) grade III IDH-mutant astrocytoma; (3) grade IV IDH-mutant astrocytoma; (4) grade IV IDH wild-type glioblastoma (GB) [3].