IDH1 and astrocytoma (excluding glioblastoma): However, there are true primary de novo IDH-mutant astrocytomas with both IDH1 p.R132 mutations and biallelic inactivation of a canonical mismatch repair gene with associated somatic hypermutation—these tumors form a distinct epigenetic cluster and represent a poor prognostic subtype of IDH-mutant astrocytoma termed “Primary mismatch repair deficient astrocytoma, IDH-mutant” [45].