REaCT-5G: a randomized trial of bone pain with 5-day filgrastim vs pegfilgrastim for neutropenia in breast cancer

BACKGROUND: Granulocyte colony-stimulating factors (G-CSFs), including filgrastim and pegfilgrastim, are associated with bone pain, potentially impacting treatment adherence. This study hypothesized that a 5-day regimen of filgrastim would result in less bone pain than single-dose pegfilgrastim in patients receiving chemotherapy for early breast cancer. METHODS: In this multicenter, open-label, randomized controlled trial, patients requiring prophylactic G-CSF during chemotherapy were randomly assigned 1:1 to receive either 5-day filgrastim or pegfilgrastim. The primary outcome was patient-reported bone pain, assessed as area under the curve of daily pain scores (0 = no pain to 10 = worst pain) over the first 5 days following G-CSF in cycle 1. Secondary outcomes included bone pain in cycles 2-4, febrile neutropenia, hospitalizations, chemotherapy delays, dose reductions, early discontinuations, chemotherapy-related deaths, health-related quality of life, and health-care resource utilization. RESULTS: From June 2021 to March 2023, a total of 233 patients were randomly assigned, with 219 analyzed (110 filgrastim and 109 pegfilgrastim) after excluding those who withdrew before receiving treatment. Adjusting for stratification factors and prespecified baseline covariates using repeated measures linear regression, the mean area under the curve (0-40) for cycle 1 bone pain was 10.2 (11.2) for 5-day filgrastim and 10.2 (9.81) for pegfilgrastim, with an adjusted mean difference of 0.70 (95% confidence interval = 1.62 to 3.02; P = .556). Although no clinically significant differences were observed in most secondary outcomes, the 5-day filgrastim group exhibited a numerically higher incidence of febrile neutropenia (6.4% vs 0.9%, P = .065) and hospitalization (10.0% vs 3.7%, P = .106). CONCLUSION: There was no significant difference in bone pain between 5-day filgrastim and pegfilgrastim.