IDH2 and oligodendroglioma: Oligodendroglioma, genetically defined by mutation in the metabolic enzyme isocitrate dehydrogenase 1 (IDH1) or 2 (IDH2) gene and an unbalanced translocation between chromosomes 1 and 19 (1p/19q-codeleted),1,2 is a rare primary brain tumor diagnosed in approximately ~1000 patients each year in the United States.