Additionally, the 2016 CNS WHO included molecular features to further classify gliomas.5,6 In the 2016 CNS WHO classification, an isocitrate dehydrogenase (IDH) gene mutation was used to subdivide GBM into 2 groups: primary GBM (IDH-wild-type) and secondary GBM (IDH-mutant). The gene discussed is IDH3A; the disease is glioblastoma.