Abstract PS1-05-12: Primary G-CSF Prophylaxis in Sacituzumab Govitecan-Treated mTNBC: Real-World Evidence from a Multinational Cohort

Abstract Background. Sacituzumab govitecan (SG) has emerged as a key agent in the treatment of metastatic triple-negative breast cancer (mTNBC), with use increasingly shifting toward earlier treatment lines. Consequently, the number of patients exposed to SG will continue to grow. Although recent updates to the SG summary of product characteristics list granulocyte colony-stimulating factor (G-CSF) primary prophylaxis as an option, the need for its routine use in all patients remains uncertain. We aimed to evaluate the impact of G-CSF primary prophylaxis on clinical outcomes and treatment-related toxicities in a multinational real-world cohort of patients with mTNBC treated with SG. Methods. Baseline characteristics were balanced with respect to prior systemic treatment for early-stage disease, the number of previous treatment lines in the metastatic setting, comorbidities, metastatic sites, and prior episodes of febrile neutropenia. However, ECOG performance status of 0 was more frequent in the prophylaxis group (50% vs. 37.1%, p=0.034). Efficacy endpoints included progression-free survival (PFS) and overall survival (OS), analyzed using the Kaplan-Meier method. Adverse events were assessed according to CTCAE criteria. All analyses were conducted using Stata Statistical Software version 19.0. Results. G-CSF primary prophylaxis was not associated with improved clinical outcomes. Median PFS was 4.2 months in the primary prophylaxis group versus 5.1 months in the no-primary prophylaxis group (p=0.20), with 6-month PFS rates of 38.5% vs. 42.1%, respectively. Median OS was 10.9 vs. 11.6 months (p=0.95), and 12-month OS rates were 44.9% vs. 47.1%, respectively. There were no statistically significant differences in the rates of all-grade toxicities between groups. Grade ≥3 neutropenia occurred less frequently in patients receiving G-CSF primary prophylaxis (33.0% vs. 50.7%, p=0.005), but this was not accompanied by a reduction in febrile neutropenia rates (4.0% vs. 4.4%, p=1.00). Rates of other all grade adverse events—including anemia, diarrhea, nausea, vomiting, and alopecia—were similar between groups. Dose reductions due to toxicity occurred in 36.0% of the prophylaxis group and 38.4% of the non-prophylaxis group (p=0.71). Among those who did not receive G-CSF primary prophylaxis, 74.4% eventually required secondary G-CSF support. Ultimately, only 17.2% of patients were treated with SG without any G-CSF support. Notably, SG dose reductions due to toxicity were not associated with inferior outcomes. In contrast, patients who required dose reduction had significantly longer PFS (median 6.6 vs. 3.3 months, p0.001) and numerically longer OS (median 13.0 vs. 10.7 months, p=0.12) compared to those without dose modification. Conclusions. In this large real-world cohort, primary G-CSF prophylaxis was not associated with improved survival or reduced febrile neutropenia, though it significantly reduced the incidence of grade ≥3 neutropenia. Given that the majority of patients ultimately received G-CSF as secondary prophylaxis, and considering the relatively short treatment duration in later lines, primary G-CSF prophylaxis remains a valid option in this setting. Consistent with prior reports, SG dose reductions due to adverse events were not associated with worse survival. Citation Format: Z. Bielčiková, M. Pieniążek, A. Polakiewicz-Gilowska, J. Żubrowska, M. Holánek, R. Soumarová, H. Študentová, A. Konieczna, M. Malejčíková, A. Młodzińska, K. Winsko-Szczęsnowicz, M. Lisik-Habib, A. Pękala, D. Krejčí, J. Šustr, I. Kolářová, I. Danielewicz, M. Szymanik-Resko, T. Ciszewski, L. Rusinova, B. Czartoryska-Arłukowicz, A. Łacko, R. Pacholczak-Madej, M. Jarzab, M. Püsküllüoğlu, M. Kubeczko. Primary G-CSF Prophylaxis in Sacituzumab Govitecan-Treated mTNBC: Real-World Evidence from a Multinational Cohort abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-05-12.