The co-occurrence of TP53 and IDH mutations is seen in the large majority of lower-grade (WHO grades II-III) diffuse astrocytomas, as well as secondary GBMs (WHO grade IV) and defines a lineage of IDH mutated tumors distinct from 1p/19q co-deleted oligodendrogliomas [11, 34]. This evidence concerns the gene IDH1 and oligodendroglioma.