They are subclassified based on key molecular alterations, namely isocitrate dehydrogenase (IDH) mutation and codeletion of the 1p and 19q chromosomal arms (1p/19q codeletion)2, falling into 3 primary groups: 1) IDH-wildtype glioblastoma, 2) IDH-mutant, 1p/19q co-deleted oligodendroglioma, and 3) IDH-mutant, 1p/19q non-codeleted astrocytoma3,4. Here, IDH1 is linked to oligodendroglioma.