Low-Dose Cyclophosphamide versus Intermediate-High-Dose Cyclophosphamide versus Granulocyte Colony-Stimulating Factor Alone for Stem Cell Mobilization in Multiple Myeloma in the Era of Novel Agents: A Multicenter Retrospective Study

The optimal stem cell (SC) mobilization strategy for patients with multiple myeloma (MM) remains a matter of debate. Possible approaches include low or high doses of cyclophosphamide (Cy), other chemotherapeutic agents, or granulocyte colony-stimulating factor (G-CSF) alone. The scope of the study was to compare low-dose Cy plus G-CSF versus intermediate-high-dose Cy plus G-CSF versus G-CSF alone for SC mobilization in MM, in terms of efficacy and safety. We retrospectively analyzed 422 MM patients undergoing SC mobilization in 6 Italian centers, including 188 patients who received low-dose Cy (LD-Cy group, defined as 2 g/m²), 163 patients who received intermediate-high-dose Cy (HD-Cy group, defined as ≥ 3 g/m²), and 71 patients who received G-CSF alone (G-CSF group). The median peak of circulating CD34+ cells was 77/µL in the LD-Cy group, 92/µL in the HD-Cy group, and 55/µL in the G-CSF group (P = .0001). The median amount of SCs collected was 9.1 × 10⁶/kg, 9.7 × 10⁶/kg, and 5.6 × 10⁶/kg in the 3 groups, respectively (P = .0001). The rate of mobilization failure (defined as failure to collect ≥2 × 10⁶/kg) was 3.7% in the LD-Cy group, 3.4% in the HD-Cy group, and 4.3% in the G-CSF group (P = .9). The target SC dose of at least 4 × 10⁶/kg was reached in 90.4%, 91.1%, and 78.6% of the patients in these 3 groups, respectively (P = .014). The "on demand" use of plerixafor was higher in the G-CSF group (76%) compared with the LD-Cy group (19%) and the HD-Cy group (6%). In multivariate analysis, G-CSF mobilization and previous use of melphalan or radiotherapy were independently associated with failure to collect the target SC dose of ≥4 × 10⁶/kg. No impacts of age, blood counts, or previous treatment with lenalidomide, bortezomib, or carfilzomib were observed. Our results suggest that LD-Cy may be considered for successful SC mobilization in patients with MM.