CC-486, the oral formulation of azacitidine (AZA), is an epigenetic modifier and DNA methyltransferase inhibitor in clinical development for treatment of hematologic malignancies. CC-486 administered for 7 days per 28-day treatment cycle was evaluated in a phase 1 dose-finding study. AZA has a short plasma half-life and DNA incorporation is S-phase-restricted; extending CC-486 exposure may increase the number of AZA-affected diseased target cells and maximize therapeutic effects. Patients with lower-risk myelodysplastic syndromes (MDS) received 300 mg CC-486 once daily for 14 days (n=28) or 21 days (n=27) of repeated 28-day cycles. Median patient age was 72 years (range 31-87) and 75% of patients had IPSS Intermediate-1 risk MDS. Median number of CC-486 treatment cycles was 7 (range 2-24) in the 14-day dosing schedule and 6 (1-24) in the 21-day schedule. Overall Response (complete or partial remission, red blood cell [RBC] or platelet transfusion independence [TI], or hematologic improvement, (IWG 2006) was attained by 36% of patients receiving 14-day dosing and 41% receiving 21-day dosing. RBC TI rates were similar with both dosing schedules (31 and 38%, respectively). CC-486 was generally well-tolerated. Extended dosing schedules of oral CC-486 may provide effective long-term treatment for patients with lower-risk MDS.