IDH1 and oligodendroglioma: Adult-type diffuse gliomas are primary brain tumors, typically molecularly classified into three subtypes: glioblastoma, IDH-wildtype (CNS WHO grade 4); oligodendroglioma, IDH-mutant, and chromosome 1p/19q co-deletion (CNS WHO grades 2–3); and astrocytoma, IDH-mutant (CNS WHO grades 2–4); each of which can be further classified into molecular subtypes [1].