Programmed Cell Death Ligand 1(PD-L1) Expression in Molecular Subtypes of Breast Cancer

Background: Tumor infiltrating lymphocytes and programmed cell death ligand 1 (PD-L1) are un- classic prognostic indicators for breast cancer, they are major players in the immune response. Binding of Programmed cell death protein (PD-1) with PD-L1 plays an important role in the immune suppression and the process of tumor escape.
Objective: To evaluate the expression of PD-L 1 in mammary invasive duct carcinoma and its correlation with molecular subtypes and other histopathological parameters.
Patients and methods: Fifty paraffin blocks were included. Histopathological examination of H&E and PD-L1 immunostained sections were done. Scores of PD-L1expression: intra tumoral and in the tumor infiltrating lymphocytes (TILs) were evaluated. Molecular subtypes and other classic prognostic parameters were assessed (Tumor size, grade, stage, lympho vascular invasion (LVI) and in situ component).
Results: PD-L1 expression in TILs was more frequent than intra tumoral expressionin various molecular subtypes. However, intra tumoral PD-L1 expression was associated with increasing tumor size, grade, the high level of TILs, LVI and molecular subtypes with special trend in Triple Negative Breast Cancer (TNBC) subtype. TNBC achieved the highest relative ratio of positive PD-L1 expression in both: intra tumoral and in TILs.
Conclusion: PD-L1 expression was more pronounced in TILs (immune cells) as compared with tumoral cells in all molecular subtypes of breast cancer with maximum ratio in TNBC. These results provide a promising future of PD-L1 as a target therapeutic option.