IDH1 and oligodendroglioma: IDH mutations define a distinct subset of GBM with a favorable outcome.1,4,19,20 These mutations are more common in lower grade gliomas such as grade II and grade III astrocytomas and oligodendrogliomas, than in GBM.1,4,19 Survival of GBM patients with such IDH-mutated tumors is more favorable than for nonmutated grade II astrocytoma, emphasizing the strong prognostic value of this marker.19 Because of the WHO 2016 reclassification of the definition of GBM into IDH-wild-type and IDH-mutant GBM,18 nomograms for GBM patients should be developed separately for these 2 unique entities.