ATRX and oligodendroglioma: The latter is most relevant for the category of diffuse glioma that is not clearly of pure astrocytic or pure oligodendroglial subtype, either in the setting of a small biopsy in which selective sampling may be a concern or because of lack of molecular studies being performed, a discordance between morphology and molecular studies (eg, a histologically classic oligodendroglioma that lacks 1p/19q co‐deletion or shows ATRX loss), or a molecular pattern that does not fit neatly into a single tumor type.