Fathi AT, et al. - Enasidenib mesylate, a mutant isocitrate dehydrogenase 2 (IDH2) protein inhibitor that promotes differentiation of leukemic myeloblasts, was recently approved by the US Food and Drug Administration for use in relapsed/refractory (R/R) mutant IDH2 acute myeloid leukemia (AML). Unexpected signs/symptoms of a differentiation syndrome (DS), which is known as a potentially lethal entity, were experienced by a minority of patients who received enasidenib for advanced myeloid neoplasms during the first study of enasidenib in humans. This current study entailed characterization of IDH-inhibitor–associated DS (IDH-DS) and its effective management. In approximately 12% of enasidenib-treated patients with mutant-IDH2 R/R AML, the occurrence of isocitrate dehydrogenase differentiation syndrome was noted. Furthermore, this syndrome was recognizable and was acknowledged as a potentially lethal clinical entity that requires prompt recognition and management.