IDH1 and astrocytoma (excluding glioblastoma): The 2016 WHO classification marked a significant departure from this previous morphology-alone classification, with the inclusion of chromosome 1p and 19q co-deletion as the “molecular signature” of oligodendroglioma and mutations in either IDH1 or IDH2 as the primary prognostic factor and molecular diagnostic criterion for adult astrocytomas [4,5].