IDH1 and glioma: Taken together, these three clusters can be designated based upon the 2016 WHO classification criteria as follows: 1) Oligodendroglial tumors, IDH-mutant, and 1p/19q-codeleted (WHO grades II–III) (n = 176); 2) Astrocytic gliomas/glioblastoma, IDH-mutant (WHO II–IV) (n = 251); and 3) Astrocytic gliomas/glioblastoma, IDH-wildtype (WHO grades II–IV) (n = 351) (Fig. 3).