IDH1 and astrocytoma (excluding glioblastoma): The most recent World Health Organization (WHO) criteria classifies adult malignant gliomas as astrocytoma, IDH-mutant (grades II, III, or IV), Oligodendroglioma, IDH-mutant, 1p/19q-codeleted (grades II, III), and Glioblastoma, IDH-wildtype (grade IV).