Comparison between autologous and allogeneic stem cell transplantation as salvage therapy for multiple myeloma relapsing/progressing after autologous stem cell transplantation

Allogeneic stem cell transplantation (allo-SCT) offers a clinical option to young patients with multiple myeloma (MM) relapsing/progressing after autologous SCT (ASCT); however, this claim remains debatable. Thus, in this retrospective study, we analyzed 526 patients with MM who underwent SCT for MM relapsing/progressing after the prior ASCT using the registry data of the Japan Society for Hematopoietic Cell Transplantation (2001-2015) and compared overall survival (OS) between allo-SCT (n = 192) and autologous stem cell retransplantation groups (ReASCT; n = 334) based on risk factor points. Significant adverse factors for OS in all patients were (1) male sex, (2) less than partial response to SCT, (3) performance status of 2 to 4, and (4) short duration from the prior ASCT. We scored factor 2 as 1 point, factor 3 as 2 points, and factor 4 as 0, 1, or 2 points for more than 30, 9 to 30, or less than 9 months, respectively. We categorized patients into three risk subgroups based on their total points (0, 1-3, and 4-5 points), indicating the usefulness of this scoring system for prognosis prediction and treatment selection. Subgroup comparison revealed OS after ReASCT to be higher than that after allo-SCT in the intermediate-risk subgroup comprising the largest population (28.2% vs 21.5%, P <.004). We observed no significant advantages of allo-SCT over ReASCT in the low- and high-risk subgroups. These findings suggest that ReASCT is more advantageous than allo-SCT in many patients with MM relapsing/progressing after the prior ASCT. However, long-term survival patients were noted only in the allo-SCT group, and allo-SCT could exhibit clinical efficacy, particularly in the low-risk group. While further examination is warranted, allo-SCT could be a potential tool for a specific population with MM relapsing/progressing after the prior ASCT.