Allogeneic stem-cell transplantation for multiple myeloma: a systematic review and meta-analysis from 2007 to 2017

Background: Despite recent advances, multiple myeloma (MM) remains incurable. However, the appearance of allogeneic stem cell transplantation (allo-SCT) through graft-versus-myeloma effect provides a potential way to cure MM to some degree. This systematic review aimed to evaluate the outcome of patients receiving allo-SCT and identified a series of prognostic factors that may affect the outcome of allo-SCT. Patients/methods: We systematically searched PubMed, Embase, and the Cochrane Library from 2007.01.01 to 2017.05.03 using the keywords 'allogeneic' and 'myeloma'. Results: A total of 61 clinical trials involving 8698 adult patients were included. The pooled estimates (95% CI) for overall survival (OS) at 1, 2, 3 and 5 years were 70 (95% CI 56-84%), 62 (95% CI 53-71%), 52 (95% CI 44-61%), and 46 (95% CI 40-52%), respectively; for progression-free survival were 51 (95% CI 38-64%), 40 (95% CI 32-48%), 34 (95% CI 27-41%), and 27 (95% CI 23-31%), respectively; and for treatment-related mortality (TRM) were 18 (95% CI 14-21%), 21 (95% CI 17-25%), 20 (95% CI 13-26%), and 27 (95% CI 21-33%), respectively. Additionally, the pooled 100-day TRM was 12 (95% CI 5-18%). The incidences of grades II-IV acute graft-versus-host disease (GVHD) and chronic GVHD were 34 (95% CI 30-37%) and 51 (95% CI 46-56%), respectively. The incidences of relapse rate (RR) and death rate were 50 (95% CI 45-55%) and 51 (95% CI 45-57%), respectively. Importantly, disease progression was the most major cause of death (48%), followed by TRM (44%). The results failed to show an apparent benefit of allo-SCT for standard risk patients, compared with tandem auto-SCT. In contrast, all 14 trials in our study showed that patients with high cytogenetic risk after allo-SCT had similar OS and PFS compared to those with standard risk, suggesting that allo-SCT may overcome the adverse prognosis of high cytogenetic risk. Conclusion: Due to the lack of consistent survival benefit, allo-SCT should not be considered as a standard of care for newly diagnosed and relapsed standard-risk MM patients. However, for patients with high-risk MM who have a poor long-term prognosis, allo-SCT may be a strong consideration in their initial course of therapy or in first relapse after chemotherapy, when the risk of disease progression may outweigh the transplant-related risks. A large number of prospective randomized controlled trials were needed to prove the benefits of these therapeutic options.