Stem cell mobilization with G-CSF and on-demand plerixafor in newly diagnosed multiple myeloma patients treated with daratumumab: a single-center experience

Introduction Daratumumab-containing induction therapy improves treatment response in transplant-eligible patients with newly diagnosed multiple myeloma but may impair hematopoietic stem cell mobilization. We evaluated the effect of daratumumab exposure on stem cell mobilization and collection and assessed the effectiveness of on demand plerixafor in patients with inadequate mobilization. Methods We retrospectively analyzed 215 transplant-eligible patients with newly diagnosed multiple myeloma treated at a single center between January 2022 and February 2025. Patients underwent granulocyte colony-stimulating factor–based mobilization, with plerixafor administered on demand on the fourth day of mobilization. The primary endpoint was peripheral blood CD34+ cell concentration on day 4 of mobilization. Secondary endpoints included plerixafor use, number of apheresis procedures, total CD34+ cells collected, and mobilization failure. Results Eighty-two patients received daratumumab-containing induction and 133 did not. The median peripheral blood CD34+ cell concentration on day 4 of mobilization was significantly lower after daratumumab exposure than without (9.61 vs 20.0 × 10 6 cells/L; P < 0.001). Plerixafor was required in 74.4% versus 39.8% of patients, respectively (P < 0.001). Among patients who received plerixafor, the median peripheral blood CD34+ cell concentration increased from 9.46 to 42.8 × 10 6 cells/L, with a comparable increase regardless of prior daratumumab exposure. Total CD34+ cells collected were lower after daratumumab exposure (mean 5.96 vs 6.98 × 10 6 cells/kg; P = 0.005), whereas mobilization failure remained uncommon (6% vs 4%). Conclusion Daratumumab-containing induction is associated with impaired stem cell mobilization and an increased need for plerixafor. On demand plerixafor effectively overcomes poor mobilization, enabling successful stem cell collection in the vast majority of patients.