Recently, long-term results from the observation arm of the RTOG 9802 (patients with age <40 years and complete resection) confirmed different survival outcomes for IDH-mutant astrocytomas compared to IDH-mutant 1p19q oligodendrogliomas (median PFS 2.8 years vs. 8.3 years, p < 0.001) in a cohort of untreated patients. The gene discussed is IDH2; the disease is oligodendroglioma.