Abstract PS5-05-16: From Keynote522 to real world evidence: The use of Pembrolizumab in early triple-negative breast cancer

Abstract The KEYNOTE-522 trial demonstrated significantly higher rates of pathological complete response (pCR) with the addition of pembrolizumab to neoadjuvant chemotherapy in patients with non-metastatic triple-negative breast cancer (TNBC). In this analysis, we aimed to evaluate whether real-world data support the benefit of adding immunotherapy to neoadjuvant chemotherapy for patients with early-stage TNBC. Additionally, we analyzed several subgroups to identify whether specific patient populations derive greater benefit from immunotherapy. Data were collected at the Tumor Center Regensburg. We included 160 patients diagnosed with non-metastatic TNBC between January 2020 and May 2025 at the Comprehensive Cancer Center Regensburg. Of these, 88 patients received neoadjuvant chemotherapy plus pembrolizumab, while 72 patients received chemotherapy alone. We observed pCR rates of 61.4% in the chemotherapy plus pembrolizumab group compared to 51.4% in the chemotherapy-only group, demonstrating an absolute increase of 10% favoring the addition of pembrolizumab. Subgroup analyses revealed that patients with a high Ki-67 score, particularly above 35%, achieved significantly higher pCR rates. Patients with BRCA mutations also showed markedly higher pCR rates in the pembrolizumab arm. Interestingly, younger patients demonstrated significantly higher pCR rates in both treatment arms compared to older patients. Detailed subgroup analyses will be presented. This real-world study demonstrates that the addition of pembrolizumab in routine clinical practice is associated with improved pCR rates, showing an absolute difference of 10%. Moreover, it suggests that specific subgroups may particularly benefit from immunotherapy. However, larger real-world studies are needed to enable more robust subgroup analyses. Citation Format: J. Roth, J. Albers, M. Gerken, O. Ortmann, S. Seitz. From Keynote522 to real world evidence: The use of Pembrolizumab in early triple-negative breast cancer 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 PS5-05-16.