Oligodendroglioma NOS

A tumor composed of cells resembling oligodendroglial cells (isomorphic, round nuclei) without demonstration of both IDH mutation and 1p/19q codeletion.

According to the World Health Organization Classification of Tumors of the Central Nervous System 2016, the “integrated diagnosis” of oligodendrogliomas (ODs) requires histological classification, WHO grade, and molecular information (both IDH mutation and 1p/19q codeletion) ^{1) 2)}.

An oligodendroglioma-like tumor lacking diagnostic mutations is given a “not otherwise specified (NOS)” designation, which is strongly discouraged by neuro-oncologists. When dealing with NOS ODs, care should be taken throughout to exclude CNS tumors including astrocytomas, glioblastomas, clear cell ependymoma, and dysembryoplastic neuroepithelial tumor ³⁾