IDH1 and glioblastoma: In the 2016 WHO Classification of Tumors of the CNS, GBMs have been classified as: (i) glioblastoma IDH-wildtype (about 90% of cases), which corresponds to the clinically defined primary or de novo glioblastoma and occurs in patients over 55 years of age; (ii) glioblastoma IDH-mutant (about 10% of cases), which corresponds to the clinically defined secondary glioblastoma (characterized by a history of prior lower grade diffuse gliomas) and preferentially arises in younger patients; and (iii) glioblastoma NOS, for which full IDH evaluation cannot be performed [13,17].