These include limiting the diagnosis of GBM to tumors that are IDH wild type, reclassifying previously diagnosed IDH-mutated GBMs as astrocytomas, IDH-mutated, and grade 4, and requiring the presence of IDH mutations for the classification of tumors as astrocytomas or oligodendrogliomas [53]. This evidence concerns the gene IDH1 and astrocytoma (excluding glioblastoma).