Controlled Study of Post-transplant Azacitidine for Prevention of Acute Myelogenous Leukemia and Myelodysplastic Syndrome Relapse (VZ-AML-PI-0129)

The Study Drug: Azacitidine is designed to block certain genes in cancer cells whose job is to stop the function of the tumor-fighting genes. By blocking the "bad" genes, the tumor-fighting genes may be able to work better. Study Groups: If you are found to be eligible to take part in this study, you will be randomly assigned (as in a flip of a coin) to 1 of 2 groups. * If you are in Group 1, you will receive azacitidine. * If you are in Group 2, you will not receive azacitidine. Study Drug Administration: If you are in Group 1, you will receive azacitidine through a needle under your skin on Days 1-5 of each cycle. Each cycle is 28 days long. Your dose of azacitidine may be lowered or stopped if certain side effects develop. Study Visits: About 2 or 3 days before each cycle and, if your doctor thinks it is needed, on Day 3 of each cycle and 1 time during Weeks 2 and 3 of each cycle, blood (about 4 teaspoons each time) will be drawn for routine tests. At 3, 6, and 12 months after the stem cell transplant: * You will have a complete medical history and physical exam. * Blood (about 4 teaspoons each time) will be drawn for routine tests. * You will have a bone marrow aspiration to check the status of the disease. You may come back for study visits more often if the doctor thinks it is needed. While on study, you will need to stay in Houston for about 3 months after the transplant (this is standard after stem cell transplants). Length of Study: You will be on study treatment for up to 1 year (up to 12 cycles of azacitidine). You will be taken off study early if you experience intolerable side effects or the disease gets worse. End-of-Treatment Visit: After you complete the planned treatment with azacitidine, you will have an end-of-treatment visit: * You will have a complete medical history and physical exam. * Blood (about 4 teaspoons) will be drawn for routine tests. * You will have a bone marrow aspiration to check the status of the disease. This is an investigational study. Azacitidine is FDA approved and is commercially available for the treatment of myelodysplastic syndrome. Up to 246 patients will take part in this study. All will be enrolled at MD Anderson.