Histologic GBM were themselves divided into three broad categories on the basis of isocitrate dehydrogenase (IDH) status: (1) glioblastoma, IDH-wildtype: most common in older patients, corresponded most commonly to primary GBM and encompassed approximately 90% of cases; (2) glioblastoma, IDH-mutant: most common in younger patients, corresponded most commonly to secondary GBM and encompassed approximately 10% of cases; and (3) glioblastoma, NOS, which was reserved for tumors in which full IDH testing could not be performed [50]. This evidence concerns the gene IDH3A and glioblastoma.