Evaluation of stromal tumor-infiltrating lymphocytes and immune checkpoint expression in triple-negative breast cancer treated with neoadjuvant chemotherapy with or without carboplatin

Abstract: Background: Triple-negative breast cancer (TNBC) is predominant among younger Pakistani women with advanced and biologically aggressive disease. Ethnic, genetic and environmental factors, as well as neoadjuvant chemotherapy (NACT), may affect the tumor immune microenvironment, including stromal tumor-infiltrating lymphocytes (TILs), immune checkpoint proteins expression like lymphocyte activation gene-3 (LAG-3), programmed cell death-1 (PD-1) and programmed cell death ligand-1 (PD-L1). Objectives: To investigate the expression of LAG-3, PD-1 and PD-L1 immune checkpoint proteins and evaluate their association with TILs in patients with TNBC receiving NACT with or without carboplatin. Methods: This quasi-experimental study included 54 patients with TNBC aged 24 to 45 years treated at two tertiary care hospitals in Karachi, Pakistan. Thirty-nine patients received anthracycline-taxane-carboplatin therapy (A+T+C group), whereas fifteen received anthracycline-taxane therapy (A+T group). Clinical response was assessed using Response Evaluation Criteria in Solid Tumor (RECIST) based on mammography and breast ultrasonography before and after NACT. TILs were assessed on hematoxylin and eosin-stained (H&E) post-NACT resection sections and categorized as low (0-10%), intermediate (11-40%), or high (>40%) according to international recommendations. Immunohistochemistry was performed for PD-1, PD-L1 and LAG-3 expression in tumor cells (TC) and TILs using compartment-specific proportional scoring with a 1% positivity cutoff. Associations were analyzed using chi-square/Fisher’s exact tests. Results: The A+T+C group attained a higher RECIST-based clinical response rate than the A+T group (92.31% vs. 60.0%) with a reduction in tumor size (2.67 cm, 95% CI: 2.14–3.23; p=0.001). High TILs density was significantly associated with PD-L1 expression on TC (χ² = 18.72; p < 0.001), LAG-3 expression on immune cells (IC) (χ² = 13.67; p < 0.001) and PD-1 expression on TC (χ² =  12.38; p = 0.002). No significant associations were observed with LAG-3 expression on TC, PD-L1 and PD-1 expressions on IC. Conclusion: Post-NACT TILs density was significantly associated with PD-L1 expression on TC and LAG-3 expression on IC in TNBC. Carboplatin improved the clinical response without significantly affecting the TIL density or immune checkpoint expression.