PN subtype typically arises in frontal cortex and often has PDGFRA amplification, IDH1/IDH2 mutation, and TP53 mutations; those with IDH1/IDH2 mutation—which includes most secondary GBMs arising from low-grade gliomas—have the best prognosis of any GBM subgroup, but proneural GBM without IDH mutations have perhaps the worst outcomes [3–5]. Here, IDH2 is linked to glioma.