Purpose

This study enrolled 472 participants, aged 55 or older, with a diagnosis of de novo acute myeloid leukemia (AML) or AML secondary to prior myelodysplastic disease or chronic myelomonocytic leukemia (CMML), and who have achieved first complete remission (CR)/ complete remission with incomplete blood count recovery (CRi) following induction with or without consolidation chemotherapy. The study is amended to include an extension phase (EP). The EP allows participants who are currently receiving oral azacitidine and who are demonstrating clinical benefit as assessed by the investigator, to continue receiving oral azacitidine after unblinding by sponsor until the participant meets the criteria for study discontinuation or until oral azacitidine becomes commercially available and reimbursed. In addition, all participants in the placebo arm and participants who had been discontinued from the treatment phase (irrespective of randomization arm) and continuing in the follow-up phase will be followed for survival in the EP.