Mutations in IDH2 genes (mIDH2) occur in approximately 12% of patients with acute myeloid leukemia. Enasidenib is an oral, small-molecule inhibitor of mIDH2 proteins. Enasidenib is shown to suppress the oncometabolite, 2-hydroxyglutarate, and promote differentiation of leukemic bone marrow blasts. In a Phase I dose-escalation and expansion study, 40.3% of patients with relapsed/refractory acute myeloid leukemia responded to enasidenib monotherapy, including 19.3% who achieved complete remission and 11% who proceeded to transplant. Median overall survival was 9.3 months. 2-hydroxyglutarate suppression did not predict response and mIDH2 clearance was possible, but not required for response. Patients with ≥6 co-mutations or NRAS co-mutations were less likely to attain a response. Enasidenib was safe and well tolerated with low rates of treatment-related adverse events.