Mycophenolate Sodium

This phase I trial studies the best dose of total body irradiation when given with cladribine, cytarabine, filgrastim, and mitoxantrone (CLAG-M) or idarubicin, fludarabine, cytarabine and filgrastim (FLAG-Ida) chemotherapy reduced-intensity conditioning regimen before stem cell transplant in treating patients with acute myeloid leukemia, myelodysplastic syndrome, or chronic myelomonocytic leukemia that has come back (relapsed) or does not respond to treatment (refractory). Giving chemotherapy and total body irradiation before a donor peripheral blood stem cell transplant helps kill cancer cells in the body and helps make room in the patient's bone marrow for new blood-forming cells (stem cells) to grow. When the healthy stem cells from a donor are infused into a patient, they may help the patient's bone marrow make more healthy cells and platelets and may help destroy any remaining cancer cells. Sometimes the transplanted cells from a donor can attack the body's normal cells called graft versus host disease. Giving cyclophosphamide, cyclosporine, and mycophenolate mofetil after the transplant may stop this from happening.