Allogeneic Stem Cell Transplantation in Multiple Myeloma: Risk Factors and Outcomes in the Era of New Therapeutic Options-A Single-Center Experience

Simple Summary Patients with multiple myeloma (MM) refractory to conventional treatment strategies represent an unmet medical need. Allogeneic stem cell transplantation (allo-HSCT) is a controversially discussed treatment option in MM, only used in selected patients due to its high rates of morbidities and mortality. We present a retrospective analysis of all MM patients who underwent allo-HSCT at our center during the last 10 years. In the overall cohort, and especially in patients with at least VGPR prior to allo-HSCT, remarkable long-term survival is possible. Therefore, even in the context of new treatment modalities, allo-HSCT may still offer a therapeutic option for individual MM patients.Abstract Background: Despite major treatment advances, multiple myeloma remains incurable. The outcome of patients who are refractory to immunomodulatory agents, proteasome inhibitors, and anti-CD38 monoclonal antibodies is poor, and improved treatment strategies for this difficult-to-treat patient population are an unmet medical need. Methods: This retrospective, unicentric analysis included 38 patients with relapsed/refractory multiple myeloma or plasma cell leukemia who underwent allogeneic stem cell transplantation (allo-HSCT) between 2013 and 2022. Survival outcomes, relapse incidence, and non-relapse mortality were calculated according to remission status, date of allo-HSCT, cytogenetic risk status, timing, and number of previous autologous HSCTs. Results: The median PFS was 13.6 months (95% CI, 7.7-30.4) and the median OS was 51.4 months (95% CI, 23.5-NA) in the overall cohort. The cumulative incidence of relapse at 3 years was 57%, and non-relapse mortality was 16%. The median PFS and OS were significantly longer in patients with very good partial remission (VGPR) or better compared to patients with less than VGPR at the time of allo-HSCT (mPFS 29.7 months (95% CI, 13.7-NA) vs. 6.5 months (95% CI, 2.6-17.0); p = 0.009 and mOS not reached vs. 18.6 months (95% CI, 7.0-NA); p = 0.006). Conclusion: For selected patients, allo-HSCT may result in favorable overall survival, in part by providing an appropriate hemato-immunological basis for subsequent therapies.