Busulfan, Cyclophosphamide, & Antithymocyte Globulin Followed by Stem Cell Transplant in Treating Hematologic Cancer

OBJECTIVES: Primary * To determine the incidence of grade II-IV acute graft-versus-host disease in patients with hematologic cancer or other diseases treated with a myeloablative conditioning regimen comprising targeted (steady-state concentration of 800-1,000 ng/mL) busulfan, cyclophosphamide, and anti-thymocyte globulin followed by matched unrelated donor allogeneic hematopoietic stem cell transplantation. * To determine the day +100 transplantation-related mortality in these patients. Secondary * To determine the effect of cyclophosphamide pharmacokinetic parameters on day +100 transplantation-related mortality in these patients. * To determine the ability of low-dose anti-thymocyte globulin administered on day +5 to induce activation-induced cell death of activated donor lymphocytes. * To determine the incidence of chronic graft-versus-host disease in patients treated with this regimen. * To determine event-free and overall survival of patients treated with this regimen. * To evaluate pharmacogenomic associations between genetic polymorphisms in drug disposition enzymes with the pharmacokinetics of busulfan and cyclophosphamide. OUTLINE: * Myeloablative conditioning regimen: Patients receive busulfan IV over 2 hours on days -8 to -5; cyclophosphamide IV over 4 hours on days -3 to -2; and anti-thymocyte globulin IV over 6 hours on day -3 and then over 4 hours on days -2, -1, and 5. * Allogeneic hematopoietic stem cell transplantation: Patients undergo allogeneic bone marrow or peripheral blood stem cell infusion on day 0. * Graft-versus-host-disease prophylaxis: Patients receive tacrolimus IV continuously or orally on days 6 to150, followed by an even taper to day 180 in the absence of graft-versus-host-disease. Patients also receive mycophenolate mofetil IV or orally beginning on day 6 and continuing to day 28. Patients undergo blood collection periodically during study for pharmacokinetic, pharmacogenomic, and other translational studies. Genomic DNA extracted from blood samples is analyzed by polymerase chain reaction for genetic polymorphisms in cyclophosphamide/busulfan disposition enzymes. Activated donor lymphocytes are assessed using flow cytometry to measure activation-induced cell death, as reflected by apoptosis in activated T cells. Chimerism on or around day 100 is also assessed using fluorescence in situ hybridization analysis and DNA fingerprinting. After completion of study treatment, patients are followed periodically.