A prospective, multicenter study on hematopoietic stem-cell mobilization with cyclophosphamide plus granulocyte colony-stimulating factor and 'on-demand' plerixafor in multiple myeloma patients treated with novel agents

High-dose melphalan plus autologous stem-cell transplantation (ASCT) is a standard of care for transplant-eligible patients with newly diagnosed multiple myeloma (NDMM), and adequate hematopoietic stem-cell (HSC) collection is crucial to ensure hematologic recovery after ASCT. In this prospective, observational study we evaluated HSC mobilization with granulocyte colony-stimulating factor (G-CSF), cyclophosphamide, and ‘on-demand’ plerixafor (in patients with <20×106 CD34+ cells/L after at least 4 days of G-CSF or failing to collect ≥1×106 CD34+ cells/kg after the first apheresis) in NDMM patients treated with novel agent-based induction therapy. The primary endpoint was the rate of poor mobilizers (patients collecting <2×106 CD34+ cells/kg or requiring plerixafor rescue to reach an adequate HSC harvest). Secondary endpoints included the rate of patients collecting ≥2×106 CD34+ cells/kg after plerixafor administration and the identification of factors predicting mobilization failure or plerixafor need. Overall, 301 patients (median age 60 years) were enrolled. 287/301 (95%) and 274/301 (93%) patients collected ≥2 and ≥4×106 CD34+ cells/kg, respectively, with a median of 9.9×106 CD34+ cells/kg collected. Poor mobilizers were 48/301 (16%): 34/301 (11%) required plerixafor rescue, and 14/301 (5%) failed HSC collection regardless of plerixafor. 34/38 (90%) patients receiving plerixafor collected ≥2×106 CD34+ cells/kg. Bone marrow plasmacytosis at diagnosis >60% (OR 4.14), lenalidomide use (OR 4.45), and grade 3–4 hematologic toxicities during induction (OR 3.53) were independently associated with a higher risk of mobilization failure or plerixafor need. Cyclophosphamide plus G-CSF and ‘on-demand’ plerixafor is an effective strategy in NDMM patients treated with novel agents, resulting in a high rate of HSC collection and high HSC yield.