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 <20x10(6) CD34(+) cells/L after at least 4 days of G-CSF or failing to collect >= 1x10(6) 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 <2x10(6) CD34(+) cells/kg or requiring plerixafor rescue to reach an adequate HSC harvest). Secondary endpoints included the rate of patients collecting >= 2x10(6) 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. Two hundred and eighty-seven of 301 (95%) and 274 of 301 (93%) patients collected >= 2x10(6) and >= 4x10(6) CD34(+) cells/kg, respectively, with a median of 9.9x10(6) CD34(+) cells/kg collected. Poor mobilizers were 48 of 301 (16%): 34 of 301 (11%) required plerixafor rescue, and 14 of 301 (5%) failed HSC collection regardless of plerixafor. Thirty-four of 38 (90%) patients receiving plerixafor collected >= 2x10(6) CD34(+) cells/kg. Bone marrow plasmacytosis at diagnosis >60% (odds ratio [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 (clinicaltrials gov. identifier: NCT03406091).