Cyclophosphamide and Busulfan Followed by Donor Stem Cell Transplant in Treating Patients With Myelofibrosis, Acute Myeloid Leukemia, or Myelodysplastic Syndrome

PRIMARY OBJECTIVES: I. To estimate the incidence of hepatotoxicity with a conditioning regimen of CY (cyclophosphamide)/tBU (busulfan) in patients receiving hematopoietic cell transplant (HCT). SECONDARY OBJECTIVES: I. To determine overall and non-relapse mortality at day +200 after HCT. II. To determine the peak bilirubin levels through day +20 after HCT. III. To determine the incidence of pulmonary toxicity in the form of idiopathic pulmonary syndrome (IPS). IV. To determine the rate of graft failure. V. To determine the time to engraftment. VI. To determine the rate of relapse. VII. To determine the incidence and severity of graft-versus-host disease (GVHD). VIII. To evaluate the pharmacokinetics/dynamics of BU and CY. X. To evaluate the pharmacogenomics of response, toxicity and pharmacokinetics of CY/tBU. OUTLINE: CONDITIONING REGIMEN: Patients receive cyclophosphamide intravenously (IV) on days -7 and -6 and busulfan IV over 3 hours on days -5 to -2. TRANSPLANTATION: Patients undergo allogeneic peripheral blood stem cell transplant on day 0. POST-TRANSPLANT IMMUNOSUPPRESSION: Patients receive tacrolimus IV or orally (PO) twice daily on days -1 to 200 with taper on day 56 and methotrexate on days 1, 3, 6, and 11. After completion of study treatment, patients are followed periodically.