OLIG2 and pilocytic astrocytoma: After initial optimism, Olig2 expression was not found helpful for distinguishing oligodendrogliomas from diffuse astrocytomas, nor from DNTs or pilocytic astrocytomas (although lack of Olig2 staining may aid in the diagnosis of neurocytoma or clear cell ependymoma rather than oligodendroglioma) [56, 72, 86, 93, 113].