Xiaomei Chavarría-Arriaga, Department of Medical Oncology, Hospital de Oncología, Centro Médico Nacional Siglo XXI, IMSS, Mexico City, Mexico
Rocío C. Grajales-Álvarez, Department of Medical Oncology, Hospital de Oncología, Centro Médico Nacional Siglo XXI, IMSS, Mexico City, Mexico
Raquel Valencia-Cedillo, Department of Anatomical Pathology, Hospital de Oncología, Centro Médico Nacional Siglo XXI, IMSS, Mexico City, Mexico
Abdel K. Dip-Borunda, Department of Medical Oncology, Hospital de Oncología, Centro Médico Nacional Siglo XXI, IMSS, Mexico City, Mexico
Background: Anti-human epidermal growth receptor 2 (HER2) therapies have significantly improved the survival rates of patients with HER2-positive breast cancer. Achieving a pathological complete response (pCR) following neoadjuvant treatment correlates with better prognosis, underscoring the need to identify prognostic biomarkers such as tumor stromal infiltrating lymphocytes (TILs). Objective: To analyze the expression of TILs as a prognostic marker for disease-free survival (DFS) in patients with HER2-positive breast cancer treated with neoadjuvant chemotherapy with trastuzumab. Method: This retrospective, analytical, observational cohort study included patients with HER2-positive breast cancer treated at the oncology hospital between January 2018 and December 2021. Histopathological slides were reviewed to determine the proportion of TILs. DFS and overall survival (OS) were estimated using the Log-Rank test and Kaplan-Meier method. The association between categorical variables was assessed with Pearson’s χ² test. A p < 0.05 was considered statistically significant. Results: One hundred and twenty-one patients were included. The DFS was 72.6 versus 61.9 months (hazard ratio [HR] 0.79, p = 0.006), and OS was 76.7 versus 66.1 months (HR 0.83, p = 0.015) in patients with TILs ≥ 10% compared to those with < 10%, respectively. The pCR rate was higher in the group with TILs ≥ 10% (p = 0.03). Conclusions: The presence of TILs ≥ 10% in patients with HER2-positive breast cancer treated with neoadjuvant chemotherapy and trastuzumab was associated with increased DFS, OS, and pCR rates.