IDH1 and glioblastoma: As a consequence, it is currently included as a histological variant of “classic” IDHwt GBM in the last 2016 WHO classification system, even when there is some evidence that gcGBM presents different clinical characteristics (younger patients) and improved prognosis (overall and progression-free survival) over GBM.4–6 However, although the rarity of IDH mutation in gcGBM reinforces the current classification, it should be noted that the giant cell phenotype can also appear in IDH-mutated tumors.