IDH1 and oligodendroglioma: In the 2021 WHO classification of tumors of CNS, adult-type diffuse gliomas were classified into the following three categories based on IDH mutations: astrocytoma IDH-mutant, oligodendroglioma IDH-mutant and 1p/19q codeleted, and glioblastoma IDH-wild. In addition to the traditional morphological characteristics, the new classification placed more emphasis on molecular diagnosis.