Real-world survival outcomes with pembrolizumab plus chemotherapy in advanced triple-negative breast cancer: Multicenter evidence from Poland, the Czech Republic, and Slovakia.

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e13118 Background: In KEYNOTE-355, pembrolizumab plus chemotherapy improved efficacy versus chemotherapy alone in first-line advanced triple-negative breast cancer (TNBC) with programmed death-ligand 1 (PD-L1) combined positive score (CPS)≥10 (median progression-free survival [mPFS] 9.7 vs 5.6 months [mo]; median overall survival [mOS] 23.0 vs 16.1 mo). Given limited real-world evidence we evaluated survival outcomes of pembrolizumab-chemotherapy across 20 oncology centers in Poland, the Czech Republic and Slovakia. Methods: This multicenter observational study, CEBCC-101, included patients with advanced TNBC and CPS≥10 treated with first-line pembrolizumab plus chemotherapy in routine practice. Primary endpoints were OS and PFS. Survival functions were estimated by Kaplan–Meier methodology. Associations between selected clinicopathologic variables and OS/PFS were explored using univariable and multivariable Cox proportional hazards models. Patients initiated treatment through June 2025; the data cutoff was November 2025. Results: The cohort included 178 female patients with median age 58.1 years (IQR 49–67, range 28–86). Median follow-up was 13.2 months (IQR: 8.6-19.5; range 0.7-38.5). In Kaplan-Meier analysis, 73 OS events occurred; estimated OS rates at 3, 6, 9, 12, 15, 18, 21, and 24 months were 97.2%, 89.9%, 83.1%, 72.9%, 66.0%, 61.2%, 48.8% and 45.1%, respectively, with mOS of 20.4 months. For PFS, 120 events occurred; estimated PFS rates at 3, 6, 9, 12, 15, 18, 21, and 24 months were 91.6%, 68.9%, 48.4%, 36.7%, 32.7%, 28.7%, 27.3% and 23.5%, respectively, with mPFS of 8.5 months. The objective response rate was 55.1% (97/176) and the disease control rate was 87.5% (154/176). In multivariable analysis for OS, presence of visceral metastases was associated with higher mortality risk (HR 2.024; 95% CI 1.162–3.525; p = 0.013). In multivariable analysis for PFS, longer time to metastatic diagnosis (HR 0.934 per year; 95% CI 0.881–0.990; p = 0.022) and de novo metastatic disease (HR 0.572; 95% CI 0.369–0.885; p = 0.012) were associated with lower risk of progression/death. Conclusions: In this Central European cohort, the observed real-world survival outcomes are consistent with those reported in the registration trial. To our knowledge, this is the first real-world evidence including mature OS estimates for pembrolizumab-chemotherapy in this setting. Visceral metastases were independently associated with worse OS. Longer time from initial diagnosis to metastatic disease and de novo metastatic presentation were independently associated with improved PFS. These findings support the effectiveness of pembrolizumab-chemotherapy in routine practice and suggest the prognostic relevance of metastatic pattern and disease-free interval in patients with advanced TNBC.

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