Recent developments in hematopoietic stem cell transplantation for multiple myeloma.

Multiple myeloma (MM) is often successfully controlled with conventional chemotherapy; however, complete remissions are uncommon, and cure is rare. High-dose therapy followed by administration of autologous or allogeneic stem cells, used for the treatment of MM in the past 15 years, is promising as a means of increasing remission rates and improving survival. Autologous transplantation has not always demonstrated survival benefits in randomized studies because most of the patients receiving transplants have relapses, whereas patients given conventional therapy can receive salvage transplants when relapse occurs. Efforts to improve the results of autologous transplantation include targeted radiation, tandem transplantation, and posttransplantation immunotherapy. Only allogeneic hematopoietic stem cell transplantation is potentially curative, owing to a graft-versus-myeloma effect. Although patients who receive either allogeneic or autologous stem cell transplants for MM have similar 3- to 5-year survival rates, only allograft recipients appear to enjoy long-term disease-free survival. High transplantation-related mortality associated with allogeneic stem cell transplantation is currently the major limitation to wider use of this potentially curative modality. Strategies designed to improve the therapeutic index of allografts include the use of nonablative conditioning regimens, peripheral blood cells rather than bone marrow, graft engineering, and targeted conditioning therapies, such as bone-seeking radioisotopes.