Abstract PO2-12-12: REaCT 5G: A randomized study comparing bone pain after 5 days of filgrastim or one day of pegfilgrastim for primary febrile neutropenia prophylaxis during neo-/adjuvant chemotherapy for early breast cancer

Abstract Background: Granulocyte colony stimulating factor (G-CSF) such as filgrastim (FIL) or pegfilgrastim (PEG) significantly reduces the risk of febrile neutropenia (FN) and treatment-related hospitalization in patients with early breast cancer receiving chemotherapy. However, patients receiving G-CSF can experience clinically significant bone pain. Previous studies examining post-GCSF bone pain were mostly based on physician pain assessment and compared mixed doses (30/60/100 μg/kg) of PEG vs. FIL (5μg/kg/day or 300 μg/day) given for 7 to 14 days. Based on a randomized non-inferiority study, 5 days of FIL is considered non-inferior to 10 days of FIL to prevent FN and hospitalizations and is frequently used in patients receiving chemotherapy for breast cancer. Patient-reported bone pain after 5 days of FIL vs. single dose of PEG has never been compared in a prospective randomized study and has important implications for patient and physician treatment preferences. Methods: In this multicenter, open-label trial, patients receiving neo-/adjuvant chemotherapy for early-stage breast cancer requiring primary FN prophylaxis with G-CSF were randomized 1:1 to either 5 days of FIL (300 μg or 480μg if ≥ 90 kg) or 1 day of PEG (6 mg) with each cycle of chemotherapy. The primary endpoint was bone pain using area under the curve (AUC) of the daily pain score from days 1-5 (AUC score 0 to 40) during cycle 1. We used linear regression adjusting for stratification factors [cancer center (2 centers) and chemotherapy regimen (taxane (TAX) or anthracycline (ANTH)-based during cycle 1] and prespecified baseline covariates: age, pain, and use of pain medications pre-chemotherapy. Supportive analysis of bone pain across cycles 1 to 4 was conducted using repeated linear regression. Key secondary endpoints included incidence of FN, hospitalizations, chemotherapy delay, dose-reduction or discontinuation, and chemotherapy-related deaths. Results: From June 2021 to March 2023, 233 patients were enrolled, with 217 patients (108 FIL/109 PEG) in the intention-to-treat analysis; 16 (7.4%) patients were excluded because of incomplete follow-up. Participants were mean age 55.6 years; almost exclusively female (99.1%), on chemotherapy regimen TAX 57% vs. ANTH 43%, had mean baseline pain score 1.12, and prevalence of pain medication use pre-chemotherapy was acetaminophen 14.7%, non-steroidal anti-inflammatory drugs (NSAIDs) 6.0% and opioids 3.2%. Characteristics were balanced between arms (Table 1). After repeated measures linear regression adjusted for age, chemotherapy regimen, baseline pain, and use of pain medications pre-chemotherapy, mean AUC for bone pain at cycle 1 was 10.94 for FIL and 10.12 for PEG (mean difference 0.82; 95% CI: -1.59, 3.23; p = 0.516). There was no significant difference between arms across treatment cycles (interaction p = 0.785; mean time-averaged difference 0.28; 95% CI: -1.75, 2.32). Across cycles 1 to 4, mean peak pain over 5 days post-GCSF was 3.27 vs. 3.41 (p=0.700); frequency of bone pain during first 8 days (pain score > 0) was 52.5% vs. 51.3%; p=0.358, and mean frequency of severe pain (pain score ≥ 5) was 17.5% vs. 15.2%; p=0.014 for FIL vs. PEG, respectively. The incidence of FN [4.6% vs. 0%, absolute difference 4.6% (95% CI: -0.3%, 9.5%; p=0.069)] and hospitalization [FN and non-FN related: 10.2% vs. 1.8%, absolute difference of 8.4% (95% CI: 1.2%, 15.5%; p=0.021)] was higher in the FIL group. There were no significant differences in chemotherapy delay (13% vs. 11%; p=0.815), dose reduction (14.8% vs. 14.7%; p=0.999), early discontinuation (8.3% vs. 5.5%; p=0.580), or chemotherapy-related death (0.9% vs. 0%; p=0.996) in the FIL vs. PEG groups, respectively. Conclusion: There was no difference in patient-reported bone pain after 5 days of FIL or PEG, even after controlling for important clinical factors. Importantly, the study observed higher rates of FN and hospitalizations in patients receiving FIL for 5 days only. Table 1 Baseline Characteristics Citation Format: Terry Ng, Yuxin Zhang, Carol Stober, Jennifer Shamess, Natalie Mills, Stuart Nicholls, Mohammed Ibrahim, Daniel Davoudpour, Christopher Armiento, Marie-France Savard, Moira Rushton, Arif Awan, Sandeep Sehdev, John Hilton, Xinni Song, Rakesh Goel, Fiona Macdonald, Kelly Daigle, Lisa Vandermeer, Monica Taljaard, Mark Clemons. REaCT 5G: A randomized study comparing bone pain after 5 days of filgrastim or one day of pegfilgrastim for primary febrile neutropenia prophylaxis during neo-/adjuvant chemotherapy for early breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-12-12.