Retrospective Study to Compare Outcomes in 159 Patients Undergoing First Autologous Stem Cell Transplantation for Myeloma Treated with Melphalan 140 mg/m2 or 200 mg/m2

Background: The standard conditioning regimen for autologous stem cell transplantation (ASCT) in multiple myeloma (MM) is 200 mg/m2 of melphalan (Mel200). Dosing is reduced by 30% (Mel140) in frail patients. Studies comparing the performance of these regimens report inconsistent findings, mainly confounded by non-consecutive patient inclusion, missing data, and heterogenous practices. The largest study reported an increased risk of death with Mel200 among patients with very good partial remission, or better, before ASCT. This retrospective study from a single center compared outcomes of patients with a first ASCT for myeloma treated with melphalan 140 mg/m2 or 200 mg/m2. Material/Methods: This was a retrospective real-world analysis from a single center. Data from 159 consecutive, first, single ASCTs for MM between 2012 and 2021 were included. Mel200 and Mel140 were administered to 131 and 28 patients, respectively. Primary and secondary objectives were overall survival (OS) and progression-free survival (PFS), respectively. Results: Median follow-up was 5.8 years. Over 90% received bortezomib-based induction, and over 76% achieved at least very good partial remission (VGPR) before ASCT in either group. PFS estimates were similar between groups (P=0.49). OS was longer with Mel200 (HR=0.42, P=0.002). Mel200 maintained OS superiority in all relevant subgroups. Conclusions: In a homogenous population of patients with MM, Mel200 was associated with longer OS, likely reflecting the physiological state of patients and tolerance to subsequent treatments. Concerns reported from EBMT data regarding the association of Mel200 with mortality among patients with VGPR or better before ASCT are not supported by this study's findings.