BACKGROUND: Sacituzumab govitecan (SG) is approved for metastatic triple-negative breast cancer in ≥ 2 line setting at 10 mg/kg IV on Days 1 and 8 (21-day cycle). Trials confirmed its superiority over 8 mg/kg with manageable safety. In practice, precautionary dose reductions are used despite no formal guidance. In Poland, fixed 200 mg vials and unreimbursed drug waste lead to early dose adjustments. METHODS: This retrospective study evaluated the impact of initial SG dose reduction on treatment outcomes and tolerability in Polish patients. Medical records provided data on baseline features, treatment, survival, and safety. Kaplan-Meier and chi-square tests were used for survival and group comparisons. A multivariate Cox model assessed the independent effect of dose reduction on overall survival (OS) and progression-free survival (PFS). Significance was set at p < 0.05. RESULTS: Among 83 patients (median age 55, range 30-86), initial dose reductions ≥ 10% were observed in 16 patients (19.3%), including 9 (10.8%) with dose reduced ≥ 20%. Administrative adjustments (reductions > 10% to flat doses of 200 mg multiplications) accounted for 18.1% of the entire cohort. Grade ≥ 2 and ≥ 3 adverse events occurred in 83.1% and 56.6%, respectively. In a multivariate analysis, a ≥ 20% initial dose reduction remained an independent predictor of shorter PFS (HR: 2.6; 95% CI: 1.1-6.6; p = 0.04) and OS (HR: 6; 95% CI: 2-17.5; p = 0.001). Initial dose reduction did not affect toxicity. CONCLUSIONS: In this preliminary report initial dose reduction of SG negatively impacted PFS and OS without reducing toxicity, highlighting the need for further studies and dosing policy adjustments.

Breast Cancer Unit Gliwice Branch Maria Skłodowska Curie National Research Institute of Oncology Gliwice 44 102 Poland

Department of Anatomy Jagiellonian University Medical College Świętej Anny 12 Krakow 31 008 Poland

Department of Clinical Oncology Kraków Branch Maria Sklodowska Curie National Research Institute of Oncology Kraków Poland

Department of Clinical Oncology Oncology Center Prof Franciszek Lukaszczyk Memorial Hospital Bydgoszcz 85 796 Poland

Department of Gynecological Oncology Maria Sklodowska Curie National Research Institute of Oncology Garncarska Street 11 31 115 Krakow Branch Poland

Department of Oncology 1st Faculty of Medicine Charles University General University Hospital Prague Czech Republic

Department of Oncology Wrocław Medical University Plac Hirszfelda 12 Wrocław 53 413 Poland

Lower Silesian Comprehensive Cancer Center Plac Hirszfelda 12 Wrocław 53 413 Poland

Surgical Oncology Oncology Centre Ludwik Rydygier Collegium Medicum in Bydgoszcz Nicolaus Copernicus University in Torun Bydgoszcz 85 067 Poland

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