Outcome of Multiple Myeloma Patients Undergoing Allogeneic Stem Cell Transplant with Post-Transplant Cyclophosphamide - a Single Center Experience

Objective The survival of multiple myeloma (MM) patients has improved significantly in the past decade with the development of new effective treatments including immunomodulators, monoclonal antibodies, and chimeric antigen receptor T cell (CAR-T) therapy. However, to date, none of the available treatments is curative for MM. In high-risk and relapsed patients, allogeneic stem cell transplant (allo-SCT) achieved long term survival in carefully selected MM patients. Here, we report our experience in MM patients who received allogeneic stem cell transplant (allo-SCT) at Thomas Jefferson University Hospital (TJUH). We aim to define the role of allo-SCT in the new era of MM treatment. Method We retrospectively analyzed 57 MM patients who received allo-SCT at TJUH from 1996-2023. We used EZR software to analyze post-transplant overall survival (OS) and disease-free survival (DFS) with Kaplan Meier method. Cumulative incidence (CI) calculated by EZR was used to determine relapse rate (RR) and non-relapse mortality (NRM). Results The median age was 53 years old. Median follow up time was 100.1 months (range from 0 to 253.6 months). Time to neutrophil and platelet engraftment data was available for 33 and 29 patients, respectively. The median time to neutrophil engraftment was 12 days (range from 3-23 days) and the median time to platelet engraftment was 16 days (range from 6-51 days). The 3-year and 5-year probabilities of OS were 53.2% (95% confidence interval 38.7%-65.7%) and 48.3% (95% confidence interval 33.9%-61.3%) respectively. The 3-year and 5-year probability of DFS were 37% (95% confidence interval 21.6%-52.5%) and 26.2% (95% confidence interval 12.6%-42%) respectively. Since 2009, most of the patients (33/36) in this study received post-transplant cyclophosphamide. The 5-years OS was 28.6% (95% confidence interval 7.8%-42.5%) and 62.7% (95% confidence interval 43%-77.2%) for patients who received allo-SCT before 2009 and after 2009 respectively (P=0.029) (Figure 1). Among 43 patients with available relapse data, the CI of relapse at 3 years was 36.9% (95% confidence interval 21.5%-52.4%) and the CI of NRM at 3 years was 26.1% (95% confidence interval 14%-39.9%). Thirty-five patients were evaluable for acute graft versus host disease (GVHD). Nine patients developed grade I-IV acute GVHD (25.7%) and 2 patients experienced grade III-IV acute GVHD (5.7%). Four out of 35 evaluable patients experienced chronic GVHD (11.4%): 2 patients had mild to moderate scleroderma, one patient had severe chronic skin GVHD and one had severe lung chronic GVHD. Conclusion In MM patients with high-risk feature or relapsed/refractory disease, allo-SCT can be curative for approximately a third of the patients. Post-transplant cyclophosphamide coupled with contemporaneous MM treatments significantly increased the survival of allo-SCT MM patients in the modern era.