IDH1 and oligodendroglioma: Histologically related malignant brain tumors that harbor mutations in IDH1/IDH2 were formerly described as glioblastoma, but since the 2021 World Health Organization classification of central nervous system tumors, they are now denoted as IDH-mutant astrocytoma (even if high-grade) or oligodendroglioma (IDH-mutant with 1p/19q co-deletion) [1,2,3].