Immunohistochemical Study on Programmed Death Ligand 1 (PD-L1) in Breast Carcinoma and Its Correlation With the Clinicopathological Parameters.

Breast cancer (BC) is considered to be the second highest cause of cancer-related death in women. Antibodies targeting programmed death ligand 1 (PD-L1) have been approved for treating breast cancer. However, PD-L1 expression and its prognostic role in BC is still the target of several researches in order to maximize its therapeutic role in different clinicopathological settings. This study aimed to evaluate PD-L1 immunohistochemical expression in both tumor cells (TCs) and tumor-infiltrating lymphocytes (TILs) in breast carcinoma in cases with and without preoperative neoadjuvant chemotherapeutic treatment and to correlate its association with clinicopathological variables and disease-free survival (DFS). Ninety cases of breast carcinoma mastectomy specimens were collected and stained immunohistochemically for PD-L1. PD-L1 expression was evaluated in TCs and TILs in the 2 settings of cases: (group A) in which the patients did not receive preoperative neoadjuvant chemotherapy (NAC) and (group B) in which the patients received preoperative NAC. The expression of PD-L1 was correlated with clinicopathological parameters. Survival analysis was conducted to correlate disease-free survival (DFS) with PD-L1 expression. In group A, 31.1% of cases showed PD-L1 expression by TCs and 47.5% showed PD-L1 expression by TILs. In group B, 13.8% of cases showed PD-L1 expression by TCs and 41.4% showed PD-L1 expression by TILs. PD-L1 expression in both TCs and TILs is significantly associated with poor prognostic factors in breast cancer. In cases with residual cancer after neoadjuvant chemotherapy, PD-L1 expression remains prominent in TILs, suggesting ongoing immune resistance.