Allogeneic Stem Cell Transplantation in Multiple Myeloma Relapsed after Autograft: A Multicenter Retrospective Study Based on Donor Availability

Allogeneic stem cell transplantation (allo-SCT) using reduced-intensity conditioning (RIC) is a feasible procedure in selected patients with relapsed multiple myeloma (MM), but its efficacy remains a matter of debate. The mortality and morbidity related to the procedure and the rather high relapse risk make the use of allo-SCT controversial. In addition, the availability of novel antimyeloma treatments, such as bortezomib and immunomodulatory agents, have made allo-SCT less appealing to clinicians. We investigated the role of RIC allo-SCT in patients with MM who relapsed after autologous stem cell transplantation and were then treated with a salvage therapy based on novel agents. This study was structured similarly to an intention-to-treat analysis and included only those patients who underwent HLA typing immediately after the relapse. Patients with a donor (donor group) and those without a suitable donor (no-donor group) were compared. A total of 169 consecutive patients were evaluated retrospectively in a multicenter study. Of these, 75 patients found a donor and 68 (91%) underwent RIC allo-SCT, including 24 from an HLA-identical sibling (35%) and 44 from an unrelated donor (65%). Seven patients with a donor did not undergo allo-SCT for progressive disease or concomitant severe comorbidities. The 2-year cumulative incidence of nonrelapse mortality was 22% in the donor group and 1% in the no-donor group (P < .0001). The 2-year progression-free survival (PFS) was 42% in the donor group and 18% in the no-donor group (P < .0001). The 2-year overall survival (OS) was 54% in the donor group and 53% in the no-donor group (P = .329). In multivariate analysis, lack of a donor was a significant unfavorable factor for PFS, but not for OS. Lack of chemosensitivity after salvage treatment and high-risk karyotype at diagnosis significantly shortened OS. In patients who underwent allo-SCT, the development of chronic graft-versus-host disease had a significant protective effect on OS. This study provides evidence for a significant PFS benefit of salvage treatment with novel drugs followed by RIC allo-SCT in patients with relapsed MM who have a suitable donor.