IDH1 and astrocytoma (excluding glioblastoma): Because the term “glioblastoma’ is now reserved for adult-type, WHO grade 4 diffuse gliomas lacking IDH1/2 mutations, IDH-mutant tumors with retained 1p/19q (frequently with ATRX and/or TP53 mutation) are designated as ‘Astrocytoma, IDH-mutant’ [15, 65].