The tumor was assigned the overall classification of anaplastic oligodendroglioma, isocitrate dehydrogenase (IDH)-mutant, 1p/19q codeleted, with ATRX expression because of the regions of more aggressive heterogeneity (discrete foci of hypercellularity and increased mitotic figures) but also extensive areas of lower-grade tumor. The gene discussed is ATRX; the disease is neoplasm.