Azacitidine and Enasidenib in Treating Patients With IDH2-Mutant Myelodysplastic Syndrome

Inclusion Criteria: * Signed, informed consent must be obtained prior to any study specific procedures * Subjects with a histologically confirmed diagnosis of MDS, including both MDS and refractory anemia with excess blasts in transformation (RAEB-T) (acute myeloid leukemia \[AML\] with 20-30% blasts and multilineage dysplasia by French-American-British \[FAB\] criteria) by World Health Organization (WHO), and chronic myelomonocytic leukemia (CMML) are eligible * Subjects must have an IDH2 gene mutation (IDH2-R140 or R172) as determined by local laboratory result * (Arm A only): Subject must be hypomethylating agent naive (i.e. prior azacitidine, decitabine, SGI-110 is exclusionary). Receipt of other MDS-directed therapy such as lenalidomide is allowed * (Arm A only): Subjects with high-risk MDS (i.e. International Prostate Symptom Score \[IPSS\] intermediate-2 or high-risk; or revised \[R\]-IPSS high or very-high risk). Patients with intermediate-1 risk by IPSS or intermediate risk by R-IPSS with high-risk molecular features including TP53, ASXL1, EZH2, and/or RUNX1 mutations are also eligible * (Arm B only): Subject must be relapsed or refractory to prior hypomethylating agent therapy, defined as prior receipt of 6 cycles of HMA therapy with failure to attain a response, or relapse after prior response to HMA therapy * Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 * Serum bilirubin =\< 2 x the upper limit of normal (ULN) (except for patients with Gilb…