Efficacy of Autologous Stem Cell Transplantation for Myeloma Patients with Suboptimal Response: A Multicenter Retrospective Analysis.

Autologous stem cell transplantation (ASCT) is the standard of care for myeloma patients who achieve partial response (PR) or better after induction therapy. However, its clinical significance in patients with suboptimal response (SR) before ASCT, including stable disease (SD) and progressive disease (PD), has not been established. Additionally, functional high-risk, including SR and early PD within 12 months, was a poor prognostic factor up to now. This study aimed to evaluate the efficacy of ASCT in myeloma patients with SR in the novel agent era. This multicenter retrospective study was conducted using the Transplant Registry Unified Management Program database of the Japanese Society of Transplantation and Cellular Therapy and included 3898 transplantation-eligible patients with newly diagnosed multiple myeloma who underwent ASCT between 2007 and 2020 and were followed up until 2021. The SR rate was 4.7%, including 1.7% with PD. In survival time analysis for overall cases, a significant difference in PFS between the very good partial response (VGPR) and PR groups was observed, whereas there was no significant difference in overall survival (OS) between the VGPR and PR groups. Additionally, there was no significant difference in OS or PFS between the PR and SD groups. Therefore, we focused on the PR, SD, and PD groups, as the purpose of this retrospective study was to investigate the clinical significance of ASCT in patients with SR compared with those with PR. The median patient age was 60 years (range, 30 to 77 years). In total, 1605 (97.4%) patients received bortezomib, 561 (38.2%) received an immunomodulatory drug (ImiD), and 512 (34.9%) received both bortezomib and an ImiD. A total of 558 patients (38.0%) received reinduction therapy. There were 229 patients (37.7%) with high-risk cytogenetics (HRCA). With a median follow-up of 31.7 months, there was a significant difference in 30-month OS rates among the PR, SD, and PD groups (86.3%, 78.5%, and 39.4%, respectively; P <.001). OS was significantly shorter in the SD group compared to the PR group among the patients with HRCA (P < .001) and patients treated with reinduction therapy (P = .013). In the PD group, the 30-month OS and PFS rates were 39.4% and 17.9%, respectively. Finally, early PD within 12 months after ASCT was predictive of short OS, whereas OS without early PD even in the PD group was similar to that in the SD and PR groups. In conclusion, OS in the SR group was not always short, but SR in the HRCA and the reinduction therapy groups was predictive of short OS, so that therapeutic alternatives to ASCT are needed. OS in the PD group was significantly short, but ASCT improved clinical outcomes when early PD did not occur even in the PD group.