Glioblastoma multiforme (GBM), a WHO Grade IV astrocytoma with key features of primary and secondary tumors, represents the most common malignant primary brain tumor in adults,6 with an incidence of nearly 15,000 cases each year in the United States.7 Among GBM lesions, 90% have no missense of IDH mutations. Here, IDH2 is linked to astrocytoma (excluding glioblastoma).