IDH1 and oligodendroglioma: The fifth edition of the WHO classification of tumors of the CNS released in 2021, have led to a more biologically homogeneous categorization of gliomas into three types: astrocytoma, (IDH)-mutant (grade 2,3,4); oligodendroglioma, IDH-mutant and 1p/19q-codeleted (grade 2,3); GB, IDH-wildtype (grade 4) (4).