PD-L1 and PD-L2 constitute an important antitumor immune response. In breast cancer, their prognostic value is still to be defined. In this study, we investigate the correlation between PD-L1 and PD-L2 protein expressions with clinical and pathologic features and disease-free survival and overall survival. To assess PD-L1 and PD-L2 expressions, we conducted immunohistochemistry studies using a breast cancer tissue microarray encompassing a total of 192 breast cancer cases, stages I, II, and III, with detailed clinical and outcome data. PD-L1 expression was present in 56.6% (107/189), and PD-L2 expression was identified in 50.8% (97/191) of breast cancer cases. Younger age at diagnosis, lymph node positivity, negative estrogen receptor, and recurrence at distant sites were all associated with both PD-L1 and PD-L2 expressions. The presence of larger tumors was associated only with PD-L1 expression. In our study, PD-L1 expression was significantly associated with better overall survival (P = .04) in breast cancer patients. Despite its association with poor clinical and pathologic features, PD-L1 expression emerges as a positive prognostic biomarker in breast cancer. This survival result might be due to the presence of a strong antitumor immune response leading to PD-L1 expression.
