Optimizing Autologous Stem Cell Transplantation in Multiple Myeloma: The Impact of Intensive Chemomobilization

Most transplant-eligible multiple myeloma (MM) patients undergo autologous peripheral blood stem cell collection (PBSC) using G-CSF with on-demand plerixafor (G P). Chemomobilization (CM) can be used as a salvage regimen after G P failure or for debulking residual tumor burden ahead of autologous peripheral blood stem cell transplantation (ASCT). Prior studies utilizing cyclophosphamide-based CM have not shown long-term benefits. At our center, intensive CM (ICM) using a PACE- or HyperCVAD-based regimen has been used to mitigate "excessive" residual disease based on plasma cell (PC) burden or MM-related biomarkers. Given the lack of efficacy of non-ICM, we sought to determine the impact of ICM on event-free survival (EFS), defined as death, progressive disease, or unplanned treatment escalation. We performed a retrospective study of newly diagnosed MM patients who collected autologous PBSCs with the intent to proceed immediately to ASCT at our center between 7/2020 and 2/2023. Patients were excluded if they underwent a tandem autologous or sequential autologous-allogeneic transplant, had primary PC leukemia, received non-ICM treatment (i.e., cyclophosphamide and/or etoposide), or had previously failed G P mobilization. To appropriately evaluate the impact of ICM among those who potentially could have received it, we utilized a propensity score matching (PSM) approach whereby ICM patients were compared to a cohort of non-CM patients matched on pre-ASCT factors most strongly associated with the receipt of ICM. Of 451 patients identified, 61 (13.5%) received ICM (PACE-based, n = 45; hyperCVAD-based, n = 16). Post-ICM/pre-ASCT, 11 patients (18%) required admission for neutropenic fever and/or infection. Among 51 evaluable patients, the overall response rate was 31%; however, 46 of 55 evaluable patients (84%) saw a reduction in M-spike and/or involved free light chains. Among those evaluated with longitudinal peripheral blood flow cytometry (n = 8), 5 patients (63%) cleared circulating blood PCs post-ICM. Compared to patients mobilized with non-CM, ICM patients collected a slightly greater median number of CD34+ cells (10.8 versus 10.2 pound 106/kg, P = .018). The median followup was 30.6 months post-ASCT. In a PSM multivariable analysis, ICM was associated with