Background: MDS, a heterogeneous group of clonal myeloid malignancies, are characterized by ineffective hematopoiesis and peripheral blood cytopenias, which can often lead to red blood cell (RBC) transfusion dependence and a risk of progression to acute myeloid leukemia (AML). In early clinical trials, 14- and 21-day (d) dosing regimens of the hypomethylating agent Oral-AZA were well tolerated and induced hematologic improvement (HI) in pts with lower-risk (LR) MDS. In a phase 3 trial, Oral-AZA 300 mg QD for 21d per 28d cycle significantly improved the rate of RBC transfusion independence (TI) and induced durable HI versus placebo (PBO) in patients (pts) with LR-MDS with RBC-transfusion-dependent anemia and thrombocytopenia (Garcia-Manero, et al. J Clin Oncol 2021). Grade 3/4 cytopenias were common in the Oral-AZA arm. Given the substantial clinical benefit of Oral-AZA observed in this setting, a new phase 2/3 trial is ongoing to further evaluate the 14d Oral-AZA regimen in pts with International Prognostic Scoring System Revised (IPSS-R)-defined low or intermediate (int)-risk MDS. Methods: This ongoing, multicenter, randomized, phase 2/3 trial (CA055-026; NCT05469737) will evaluate the safety and efficacy of Oral-AZA in pts with IPSS-R low- or int-risk MDS. Key eligibility criteria include ≥ 18 years, ECOG performance status score ≤ 2, and ≥ 1 cytopenia (anemia, thrombocytopenia, or neutropenia). Pts with an absolute neutrophil count < 0.5 × 10⁹/L within a week of randomization will be excluded. Informed consent will be obtained from all participants. The phase 2 portion will enroll and randomize ~42 pts 1:1 to receive open-label Oral-AZA 200 or 300 mg QD for 14d per 28d cycle, plus best supportive care (BSC), to determine the recommended phase 3 dose (RP3D). The primary endpoints are safety and rate of complete remission (CR) within 6 Tx cycles. The secondary endpoints are overall response rate (ORR), and packed (p) RBC-TI and platelet-TI sustained for 84d in ≤ 6 Tx cycles. ORR includes CR, partial remission (PR), marrow CR, and any HI, per IWG 2006 response criteria. In the phase 3 portion, ~188 additional pts will be enrolled and randomized 1:1 to Oral-AZA at the RP3D or PBO for 14d per 28d cycle, plus BSC. Pts in the PBO arm with stable disease at Tx cycle 6 disease assessment or with documented disease progression after ≥ 3 Tx cycles will have the option to cross over into the Oral-AZA arm. The primary endpoint is CR in ≤ 6 Tx cycles. The key secondary endpoint is 84d pRBC-TI. Other secondary endpoints include those described in the phase 2 portion plus overall survival, event-free survival, time to AML progression, iron parameters, health-related quality of life, healthcare resource utilization, and safety parameters. Pts who benefit from Oral-AZA in phase 2 or 3 may continue to receive Tx in an extension phase. Trial recruitment began in December 2022 and is ongoing. Clinical trial information: NCT05469737.