IDH1 and oligodendroglioma: Based on the World Health Organization’s (WHO) classification of tumors of the fifth edition of the central nervous system (CNS) (WHO CNS5), gliomas can be classified into three types: isocitrate dehydrogenase (IDH)-mutant (mut + non-codel) astrocytoma, IDH-mutant and 1p/19q-codeleted (mut + codel) oligodendroglioma, and IDH-wildtype (IDH-wild) glioblastoma [14].