The distinction between glioblastoma, IDH-wildtype (GBM-IDHwt), and oligodendroglioma (ODG) based on somatic mutations such as those in the telomerase reverse transcriptase promoter (TERTp) and isocitrate dehydrogenase (IDH) genes is particularly noteworthy. The gene discussed is IDH2; the disease is oligodendroglioma.