Unrelated Stem Cell Transplantation After Reduced Intensity Conditioning for Patients with Multiple Myeloma Relapsing After Autologous Transplantation A Prospective Multicenter Phase II Study of the Chronic Leukemia Working Party of the European Group for Blood and Marrow Transplantation (EBMT).

Dose-reduced conditioning followed by allogeneic stem cell transplantation has become a treatment option for patients with multiple myeloma. However, the experience using unrelated donor is limited.

From 2002 to 2007, 49 myeloma patients with relapse to a prior autologous SCT were included in a prospective multicenter trial to determine the efficacy of a reduced melphalan (140 mg/m²)/fludarabine regimen followed by allogeneic SCT from unrelated donors. GvHD prophylaxis consisted of anti-lymphocyte globulin (ATG-Fresenius®), cyclopsorin A and short course of MTX.

No primary or secondary graft failure was observed and all patients showed leukocyte and platelet engraftment after a median of 15 and 19 days, respectively. Acute graft-versus-host disease (GvHD) grade II to IV occurred in 25% and chronic GvHD in 35% of the patients. Limited GvHD was seen in 29 % and extensive GvHD was seen in 6 % of the patients. Overall response rate at day 100 was 95% including 46% complete remission (CR). Cumulative incidence (CI) of non-relapse mortality at one year was 25% (95% CI: 13-37%) and significantly lower for HLA matched compared to mismatched SCT (10% vs. 53%, p=0.001). During follow-up 22 patients experienced relapse (54 %) resulting in a cumulative incidence of relapse at 1, and 3 years of 27% (95% CI: 14-40%) and 55% (95% CI: 40-70%), respectively. The median time to relapse was 318 days (r: 56 – 861). After a median follow up of 43 months, the estimated 5-year progression-free (PFS) and overall survival (OS) 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).

Allogeneic stem cell transplantation from unrelated donors after a reduced intensity regimen is feasible, but an optimal donor selection is mandatory for a low non-relapse mortality. The high relapse incidence remains a major concern should be improved by including posttransplant strategies to upgrade remission status.

No relevant conflicts of interest to declare.