Abstract PS4-10-18: Tils as a predictor of response in triple-negative breast cancer: analysis of clinical and pathological outcomes in patients undergoing neoadjuvant chemotherapy based on the keynote-522 protocol in a brazilian cancer center

Abstract Background: Triple-negative breast cancer (TNBC) tumors are aggressive, highly immunogenic, and often associated with early recurrence. Studies suggest that high levels of tumor-infiltrating lymphocytes (TILs) are associated with improved clinical outcomes, including overall survival (OS) and progression-free survival (PFS). We evaluated the presence or absence of complete pathological response (pCR) according to the TILs found in the tumor analysis of patients included in this cohort. Patients and Methods: A total of 121 patients diagnosed with clinical stage (CS) II-III TNBC who received treatment based on the KeyNote-522 protocol (pembrolizumab combined with neoadjuvant chemotherapy) from April 2022 to January 2025 were evaluated. Patients were divided into two groups with a TILs cutoff of 30 and ≤30. Subsequently, clinical outcomes of pCR, overall survival (OS), and progression-free survival (PFS) were assessed. Results: A total of 121 patients, with a median age of 44 years, were analyzed, with the majority (69%) classified as CS II and 63% being premenopausal. TILs analysis was performed in 104 patients, with 74 (71%) having TILs ≤30 and 30 (28.8%) having TILs 30.Regarding tumor characteristics, the predominant histological subtype was ductal in both subgroups (81.8%). The majority of the population had histological grade 3 (67.7%). Regarding pCR, we observed that in the TILs ≤30 subgroup, 37 patients (50%) achieved a complete response, while in the TILs 30 subgroup, 25 patients (83.3%) achieved a complete response. Patients with TILs greater than 30 had a higher likelihood of pCR (OR 0.24; p 0.01). Eight patients experienced tumor recurrence, with 7 in the TILs ≤30 subgroup.Regarding PFS and OS analysis, no statistically significant difference was observed (p = 0.58 and p = 0.88, respectively). In the TILs ≤30 subgroup, with a 40-month follow-up, the median OS was 23.5 months, and the median PFS was 21.5 months. In the TILs 30 subgroup, the median OS was 23 months, and the median PFS was 19 months. However, when analyzing the relationship between pCR and TILs, it was found that patients with TILs greater than 30 had a higher likelihood of pCR (OR 0.24; p 0.01). Conclusion: The presence of TILs greater than 30 was associated with a significant increase in pCR. The data obtained in this study suggest that tumor lymphocytic infiltrate may serve as a prognostic biomarker for pCR in patients with TNBC. However, it should be considered that the sample size was small, and further studies in this area are needed. Citation Format: F. BALINT, G. de Almeida, N. Pandolfi, M. Cesca, L. Leite, S. Sanches, E. Santos, V. Cordeiro, M. Tavares. Tils as a predictor of response in triple-negative breast cancer: analysis of clinical and pathological outcomes in patients undergoing neoadjuvant chemotherapy based on the keynote-522 protocol in a brazilian cancer center 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 PS4-10-18.