The relationship between Programmed Death Ligand-1 and tumor-infiltrating lymphocytes in triple negative breast cancers

Triple negative breast cancer (TNBC) is a subgroup of malignant breast cancers which constitutes approximately 12-20% of breast cancers. TNBC does not express estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her2/cerb-B2). In this respect, it differs from other breast cancers. There is no specific treatment method for this tumor group, where the benefits of standard chemotherapy, radiotherapy and hormone therapy are limited. Recently identified Programmed Death Protein-1/Programmed Death Ligand-1 (PD-1/PD-L1) signaling pathway is an adaptive immune resistance mechanism activated by tumor cells to evade the immune response. Studies have shown that agents targeting PD-1 or PD-L1 combined with chemotherapy have positive results in both early-stage and metastatic TNBC. Tumor-Infiltrating Lymphocyte (TIL) is another factor that has gained increasing importance in TNBC. TIL is an immune response consisting of mononuclear cells found inside the tumor or in the stroma of the tumor. The high rate of TIL in TNBC makes the tumor a potential target for immunotherapy. In this study, 62 cases of triple negative breast cancer between 2012 and 2023 were included. We evaluated PD-L1 expression by immunohistochemistry and TILs with hematoxylin-eosin. We compared the results with each other and with clinicopathological findings. We also examined the effects of the findings on overall and relapse-free survival. Mean follow-up of the cases was 38.9±28.1 months. We found a significant relationship between the presence of PD-L1 expression and TIL. PD-L1 expression was significantly associated with high TIL rate. We examined PD-L1 in tumor cells (TC) and immune cells (IC) separately and found concordance between the two groups. We demonstrated that PD-L1 IC did not affect overall survival but was associated with a significant reduction in relapse-free survival. We compared the rates of TILs with both overall and relapse-free survival, but we could not find any significant results. Among the clinicopathological findings, advanced age, segmental mastectomy, lymphovascular invasion and the presence of recurrence had an effect on overall survival. We observed that PD-L1 IC expression, histological grade, segmental mastectomy and the presence of distant metastasis had a significant effect on disease-free survival. We think that including PD-L1 and TIL evaluation in pathology reports in triple negative breast cancers may be helpful in the selection of patients who can receive treatment and in the development of new treatments.