Tbo-Filgrastim Versus Filgrastim during Mobilization and Neutrophil Engraftment in Autologous Stem Cell Transplantation

Background: While various peripheral blood stem cell (PBSC) mobilization strategies have been employed, granulocyte-colony stimulating factor (G-CSF) with or without plerixafor is widely utilized for its efficacy, safety and cost.  To date, the recombinant G-CSF known as tbo-filgrastim has not been compared to traditionally used filgrastim for mobilization of PBSC or for engraftment after autologous stem cell transplantation (ASCT).  Therefore, we sought to compare the efficacy and cost of tbo-filgrastim to filgrastim during mobilization and engraftment.

Methods: Patients with lymphoma or plasma cell disorders undergoing G-CSF mobilization, with or without plerixafor, were included in this retrospective chart review.  Patients receiving a second autologous transplant or mobilized with chemotherapy were excluded.  Tbo-filgrastim and filgrastim were given at a dose of 10 mcg/kg daily for four days prior to PBSC collection on day 5.  The adjunct use of plerixafor was determined by circulating CD34⁺ cells/µL on day 4 of mobilization.  Post-transplant, each agent was given at a dose of 5 mcg/kg daily on day +7 and continued until neutrophil engraftment. The primary outcome was total collected CD34⁺ cells/kg.  Secondary outcomes included total collection days, peripheral CD34⁺ cells/µL on day 4 of mobilization, and the adjunctive use of plerixafor. Post-transplant outcomes included time to neutrophil engraftment, the number of blood product transfusions required prior to engraftment, and events of febrile neutropenia.  Cost minimization analysis was also conducted to determine direct cost-savings between the two G-CSF products.

Results: A total of 148 patients were included in the final analysis.  Median patient age was 60 years, 81 (55%) were male and 86 (58%) received filgrastim.  Patients in the filgrastim group had a higher median age compared to those receiving tbo-filgrastim (61.5 vs 56 years, p=0.01).  There were no other statistically significant differences in patient demographics between the two groups.  Patients receiving filgrastim collected a median of 5.565 x 10⁶ CD34⁺ cells/kg compared to a median of 5.9 x 10⁶ CD34⁺ cells/kg for the tbo-filgrastim group (p=0.47).  There were no statistically significant differences in all secondary endpoints except a mean fewer days of collection in patients receiving tbo-filgrastim (1.4 vs 1.6 days, p=0.01). Patients receiving tbo-filgrastim had a mean cost savings of $761.46 per patient during mobilization and $353.46 per patient during engraftment. 

Conclusions: Tbo-filgrastim demonstrated similar CD34⁺ yield as compared to filgrastim in the setting of PBSC collection with no difference in secondary efficacy and safety outcomes.  Furthermore, tbo-filgrastim utilization was associated with cost savings of approximately $1,115 per patient.