IDH1 and glioblastoma: Recently, GBM was classified in three groups: (1) GBM, IDH-wildtype (about 90% of cases, generally corresponds to the clinical definition of primary GBM and is prevalent in patients over 55 years); (2) GBM, IDH-mutant (about 10 % of cases, corresponds closely to so-called secondary GBM and preferentially arises in younger patients); and (3) GBM, NOS (a diagnosis that is reserved for those tumors for which full IDH evaluation cannot be performed) [3].