IDH1 and gliosarcoma: In the 2016 revision of the World Health Organization’s classification of CNS tumors, the determination of IDH mutation status was introduced, distinguishing GBM subgroups, namely IDH-wild-type, IDH-mutant, and NOS (not otherwise specified) [2], with three variants of IDH wild-type, i.e., giant cell GBM, gliosarcoma, and epithelial-like GBM (Ep-GBM) [11].