The primary oligodendroglioma CNS WHO grade 2 and 3 cases (n = 12) were methylation-based classified as the oligodendroglioma, IDH-mutant and 1p/19q-codeleted subclass and 83% (10 out of 12) maintained the methylation subclass at recurrence (Fig. 1). This evidence concerns the gene IDH2 and oligodendroglioma.