Second Salvage Autologous Hematopoietic Stem Cell Transplantation in Patients with Relapsed/Refractory Multiple Myeloma in the Era of Novel Agents: Results of the KMM2301 Study

Background: Second salvage autologous stem cell transplantation (SAT) is a therapeutic option for patients with multiple myeloma (MM) who relapse after a first autologous stem cell transplantation (ASCT) in the era of novel agents. However, the clinical context in which SAT provides benefit relative to contemporary salvage regimens remains unclear. Methods: We retrospectively analyzed 51 patients who underwent SAT after novel agent-based induction and first ASCT, and salvage re-induction, and compared outcomes with 113 patients treated with salvage carfilzomib–lenalidomide–dexamethasone (KRd) without SAT. Results: Median interval from first ASCT to relapse was 27 months. In the SAT cohort, median progression-free survival (PFS) and overall survival (OS) from initiation of salvage therapy were 30 and 99 months, respectively. A time to relapse ≥18 months after first ASCT and receipt of SAT as second-line of therapy were associated with significantly longer PFS and OS. In multivariate analysis, administration of SAT at later lines was independently associated with inferior outcomes, while a time to relapse ≥18 months after first ASCT was associated with significantly longer OS. Compared with the KRd-only cohort, SAT was associated with longer OS, whereas PFS was numerically longer without statistical significance. Among patients who had received both a proteasome inhibitor and an immunomodulatory drug as salvage induction, SAT was associated with longer PFS and OS. Conclusions: SAT may provide clinical benefit in selected patients with MM, particularly those with a durable response to first ASCT and those undergoing SAT at an earlier line of relapse in the novel agent era.