Typical oligodendrogliomas are positive for IDH1 R132H unless they have a non-canonical IDH alteration, and generally show strong nuclear staining for ATRX and little to no nuclear reactivity for p53 (Fig. 4, a-d), except for anaplastic cases which can show a significant amount of p53 immunoreactivity. Here, ATRX is linked to oligodendroglioma.