Tumors with loss of ATRX expression and IDH1/2 mutations can be reliably classified as diffuse astrocytomas while IDH1/2 mutant tumors with retained ATRX expression should undergo testing for 1p/19q co-deletion to help differentiate between a diffuse astrocytoma and oligodendroglioma (21). Here, IDH1 is linked to oligodendroglioma.