Stromal Tumor-Infiltrating Lymphocytes Are Associated with Immune Checkpoint Protein Expression in Triple-Negative Breast Cancer Patients: A Subset of the Karachi Population

Background: Stromal tumor-infiltrating lymphocytes (TILs) are currently being considered as a prognostic factor in triple-negative breast cancer (TNBC); however, their association with the tumor immune microenvironment remains unclear. To address this knowledge gap, we aimed to evaluate the expression and association of Programmed cell death-1 (PD-1), its ligand programmed cell death ligand-1 (PD-L1) and lymphocyte activation gene-3 (LAG-3) checkpoint proteins with TILs in TNBC patients treated with neoadjuvant chemotherapy (NACT). Methods: Patients (n=54; aged 24-45 years) were classified into two groups: thirty-nine received anthracycline-containing taxane- (A+T group) and fifteen received anthracycline/taxane /carboplatin (A+T+C group) in combinations. Immunohistochemistry (IHC) to evaluate PD-1, PD-L1 and LAG-3 expression. Stromal TIL were assessed using hematoxylin and eosin (H&E)-stained sections from TNBC patient biopsies obtained after NACT. Results: Among the 54 TNBC patient biopsies, PD-L1 positivity on tumor cells was observed in twenty patients (66.67%) and was significantly associated with a larger tumor size (p=0.036). However, The carboplatin-based NACT regimen demonstrated a higher clinical response rate (92.31%), with significant tumor size reduction in thirty-nine patients. In the same group, PD-L1-positive tumor cells showed significant association (p-value=0.0001) in fifteen patients with high TILs (93.75%). There were intermediate levels of TILs among nineteen patients (100%) with LAG-3-positive immune cells and only ten patients (25.64%) had high TIL levels (p-value=0.0001). Conclusion: TILs are the most reliable immune markers and are significantly associated with PD-1, PD-L1 and LAG-3 in carboplatin based NACT treated group of TNBC patients. Anti-PD-1/PD-L1 and anti-LAG-3 therapy alone or in combination with chemotherapy may be promising treatments for a subset of TNBC patients.