The authors classified 133 patients from two tumor databases in three groups, according to the molecular characteristics of the tumors: Group O (IDH mutant, 1p/19q codeleted oligodendrogliomas), Group A (IDH mutant, ATRX inactivated astrocytomas), and Group G (IDH wild-type, GBM-like) [23]. This evidence concerns the gene IDH1 and oligodendroglioma.