Hematopoietic stem cell transplantation in multiple myeloma

Multiple myeloma (MM) is the second most common hematologic malignancy, affecting approximately 14,000 new patients per year in the United States. For over four decades, the standard treatment for MM has been a regimen of melphalan combined with prednisone. Using this treatment modality, complete responses are rare, and 50% of patients have had disease that was resistant to chemotherapy. Attempts have been made to improve the outcome of MM by administering combinations of i.v. poli-chemotherapy, but these treatments are equivalent in terms of overall survival. High-dose therapy with peripheral blood stem cell support can be applied safely in these patients and achieves significantly higher complete remission rates as well as better event-free survival and overall survival. However, neither tumor-cell purging, positive selection, intensification of conditioning with additional chemotherapeutic agents, nor total body irradiation have been shown to improve outcome. The role of tandem transplantation with high-dose melphalan seems to be a good selection of treatment in hospitals having all resources. Future research will include the combination of the best remission-induction regimen with tandem transplants and maintenance treatments (thalidomide, idiotype or dendritic cell vaccination) that will sustain complete remission. Development of non-myeloablative allogeneic transplantation in order to exploit the graft-versus myeloma effect provides an alternative for patients who have a compatible donor. Combining all of these modalities with the new drugs developed few years ago (thalidomide, bortezomib, revlimid), we hope that MM will become a manageable chronic disease and perhaps a curable disease at least for 30% to 40% of the patients.