IDH1 and astrocytoma (excluding glioblastoma): The evolution of WHO grading1 has increasingly incorporated molecular analysis that stratifies glioma based on isocitrate dehydrogenase (IDH) status into groups with distinct biology and clinical outcomes with mutations in IDH1/2 predicting improved survival (5–15 years, depending on grade).2–5IDH-mutated gliomas are further stratified into oligodendroglioma, which is defined by the presence of 1p19q co-deletion and astrocytoma (1p19q intact).