This update integrates molecular data into the diagnostics and classification of brain tumors, defining GBs as “diffuse astrocytic and oligodendroglial tumors” and establishing a new distinction between GB subtypes based on isocitrate dehydrogenase (IDH) mutations: IDH-wildtype (giant cell GB, gliosarcoma and epithelioid GB), IDH-mutant and NOS (not otherwise specified) [4]. This evidence concerns the gene IDH1 and gliosarcoma.