IDH1 and astrocytoma (excluding glioblastoma): In addition, IDH-mutant astrocytoma often has P53 and ATRX mutations and is often the ALT phenotype, while IDH-mutant and 1p/19q-codeleted oligodendrogliomas often have wild-type P53 and TERT promoter mutations, which are indicative of telomerase activation [11].