Expression of PD-L1 in Early-Stage Invasive Breast Carcinoma and Its Relation to Tumor-Infiltrating Lymphocytes

Immunotherapeutic targets became one of the promising approaches in breast cancer (BC), especially in advanced stage triple-negative subtype (TNBC). However, the role of programmed cell death ligand 1 (PD-L1) targeting in other BC subtypes, especially in early-stage carcinoma is less explored. We aimed in this study to investigate the prevalence of PD-L1 in early-stage invasive BC of different molecular subtypes and to elucidate its relation to tumor-infiltrating lymphocytes (TILS) density (cytotoxic and regulatory T-cells), established clinicopathological factors and patients' outcome.

One hundred and nine cases of early-stage BC were enrolled in our study. Cases were classified into five molecular subtypes according to the Immunohistochemical data. PD-L1, FOXP3 and CD8 immunostaining were analyzed for all studied cases. PD-L1 expression was correlated with CD8+ cytotoxic T-cells, FOXP3+ regulatory T-cells, histopathologic parameters, BC molecular subtypes, 7-years disease-free survival (DFS) and overall survival (OS).

PD-L1 was expressed in 11% of the studied early-stage BC cases. It showed a significant correlation with high tumor grade (p= <0.001), development of metastasis (p=0.037), high FOXP3+ T-cell density (p= <0.001) and low CD8+ T-cells density (p= <0.001). PD-L1 expression was higher in TNBC (16.1%), followed by HER2/neu-enriched group (14.3%). All luminal A cases showed negative PD-L1 expression. PD-L1 was found to be an independent prognostic factor for patients' survival (DFS; p=0.031 and OS: p=0.04).

Although the impact of PD-L1 on early-stage BC outcomes had not been clearly established, our results indicated that PD-L1 is a negative prognostic marker in early settings. PD-L1 can serve as a new therapeutic target for patients with high-grade early-stage breast carcinoma.