High-Dose Cyclophosphamide In Combination With G-CSF Versus G-CSF Alone For Mobilization Of Hematopoietic Stem Cells After Induction Therapy Including Velcade, Cyclophosphamide and Dexacort

Even in the era of novel agents, high-dose chemotherapy followed by autologous stem cell transplant (ASCT) is considered to be an essential part of treatment for young patients with multiple myeloma (MM), providing durable responses. Currently, VCD (velcade, cyclophosphamide and dexacort) is one of the most commonly employed induction regimens. High-dose cyclophosphamide (HDC), often used in stem cell (SC) mobilization in conjunction with G-CSF, is associated with adverse events and only modest efficacy against myeloma. An alternative mobilization regimen, using G-SCF alone, has been recently suggested to provide adequate SC collection with less toxicity. Nevertheless, the efficacy and safety of using G-SCF alone after VCD induction have not been fully explored. The current study compares the safety and efficacy of mobilization using HDC-G-CSF versus G-CSF alone in MM patients treated with VCD as induction therapy.

The study was approved by the Institutional Review Board of the Rambam Medical Center (Approval # 0110-13 RMB). Data on all consecutive newly diagnosed transplant-eligible MM patients, treated with VCD between 2009 and 2012, were retrospectively reviewed. Eligibility criteria were: VCD induction followed by SC mobilization, either with G-CSF or HDC-G-CSF, with subsequent high-dose melphalan (200 mg/m²) and ASCT. The mobilization protocol was chosen at the discretion of the treating physician. Evaluated data included patient characteristics, SC collection and engraftment related parameters. For statistical analysis, Mann-Whitney non-parametric test for 2 independent groups was used.

79 patients were included: 50 mobilized with HDC-G-CSF, and 29 with G-CSF alone. There were no statistically significant differences in terms of patient demographic and MM-related characteristics (MM type, ISS, number of VCD cycles, and disease status at the end of induction) between the 2 cohorts. The first day of SC collection yielded a median of 14.6x10⁶ (range 1.9 -10.1) vs 5.3x10⁶ CD34 cells/Kg (range 0.6-37.7) in the HDC-G-CSF vs the G-CSF groups (p=<0.001). A significantly higher total CD34 collection was obtained in the HDC-G-CSF treated patients (15.9 x 10⁶ vs 8.1x10⁶ CD34 cells/Kg, respectively, P<0.001).

Additionally, a bivariate analysis showed that male gender and platelet count (>150,000/mL) prior to mobilization had a significant impact on the outcome of SC collection.

The percentage of patients needing more than one day of leukopheresis following HDC-G-CSF and G-CSF was 42% and 83%, respectively. During treatment and mobilization, 20% of patients in the HDC-G-CSF cohort were hospitalized due to neutropenic fever, while none of the patients from the G-CSF group required hospitalization (P<0.011). In all patients apart from one (G-CSF group), at least the minimum of CD34 cells/Kg required to perform a transplant (2x10⁶ CD34 cells/Kg) was collected. Moreover, most patients succeeded in collecting >5x10⁶ CD34 cells/Kg (96% and 93.1% in HDC-G-CSF and G-CSF groups, respectively). Notably, the difference between the groups achieved statistical significance only in collection of >8x10⁶ CD34 cells/Kg (88% and 55.2% of patients treated with HDC-G-CSF and G-CSF, respectively).

The median amount of cells administered at transplantation was 7.9x10⁶ and 4.9x10⁶ for patients mobilized with HDC-G-CSF vs G-CSF, respectively, reflecting the difference in the total amount of collected cells. Despite the variation in the amount of transplanted cells, no significant difference in parameters of the transplant outcome was revealed between the 2 cohorts:  time to neutrophil engraftment (>500 cells/µl) at a median of 12 days in both groups and platelets engraftment (>25,000 cells/µl) at a median of 14.5 vs 13 days in the HDC-G-CSF and G-CSF groups, respectively. The length of hospitalization, approaching 17 days, did not differ between the 2 groups.

Mobilization using HDC-G-CSF results in a higher total amount of collected CD34 cells and requires less days of leukophersis. Nevertheless, G-CSF alone provides a sufficient number of SC for transplantation in almost all patients, and this approach is much safer than treatment with HDC-G-CSF. Since engraftment results are identical with the 2 mobilization methods, the use of G-CSF alone could be considered as a preferable cell mobilization protocol in patients previously exposed to VCD induction.

No relevant conflicts of interest to declare.