IDH1 and oligodendroglioma: The classification of diffuse gliomas in adults is now as follows [10]: (1) astrocytoma—isocitrate dehydrogenase (IDH) mutant, WHO grade 2–4; (2) oligodendroglioma—IDH mutant without 1p/19q co-deletion, WHO grade 2–3; (3) GBM—IDH wildtype, WHO grade 4.