Reduced-Intensity Conditioning Followed By Donor Peripheral Blood Stem Cell Transplant in Treating Patients With Multiple Myeloma

PRIMARY OBJECTIVES: I. To evaluate the efficacy of this approach by determining the 1-year progression-free survival (PFS) and overall survival (OS). II. To evaluate day 100 non-relapse mortality. III. To determine the incidences of grades II-IV acute graft-versus-host disease (GVHD) and chronic extensive GVHD. OUTLINE: PREPARATIVE REGIMEN: Patients receive fludarabine phosphate intravenously (IV) over 30 minutes on days -5 to -3 and intermediate-dose melphalan IV over 15-20 minutes on day -2. Patients also undergo low-dose TBI on day 0. TRANSPLANTATION: Patients undergo allogeneic PBSCT on day 0. IMMUNOSUPPRESSION: Patients receive cyclosporine orally (PO) twice daily (BID) on days -3 to 80 with taper to day 180 (related donors) or on days -3 to 100 with taper to day 180 (unrelated donors). Patients also receive mycophenolate mofetil PO BID on days 0-27 (related donors) or thrice daily (TID) on days 0-40 with taper to day 96 (unrelated donors). After completion of study treatment, patients are followed up at 3, 6, 12, 18, and 24 months, and then annually thereafter for 5 years.