Unrelated stem cell transplantation after reduced intensity conditioning for patients with multiple myeloma relapsing after autologous transplantation.

From 2002 to 2007, 49 myeloma patients who relapsed following autologous SCT were included in a prospective multicenter trial to determine the efficacy of a reduced melphalan/fludarabine regimen followed by allogeneic SCT from unrelated donors. All patients showed leucocyte and platelet engraftment after a median of 15 and 19 d, respectively. Grade II-IV acute graft-versus-host disease (GvHD) occurred in 25% of patients and 35% had chronic GvHD. Overall response rate at day 100 was 95% including 46% complete remission (CR). Cumulative incidence of non-relapse mortality at 1 year was 25% [95% confidence interval (CI): 13-37%] and was significantly lower for human leucocyte antigen (HLA)-matched compared to -mismatched SCT (10% vs. 53%, P = 0.001). The cumulative incidence of relapse at 3 years was 55% (95% CI: 40-70%). After a median follow up of 43 months, the estimated 5-year progression-free and overall survival rates were 20% and 26% respectively and were significantly better for matched in CR at day 100 (41% vs. 7%, P = 0.04 and 56% vs. 16%, P = 0.02). We conclude that optimal donor selection is mandatory for a low non-relapse mortality and high relapse incidence, which remains a major concern, should be improved by including post-transplant strategies to upgrade remission status.