Prognostic Value of PD‐L1 in Breast Cancer: A Meta‐Analysis

Programmed cell death 1 ligand 1 (PD‐L1) is a promising therapeutic target for cancer immunotherapy. However, the correlation between PD‐L1 and breast cancer survival remains unclear. Here, we present the first meta‐analysis to investigate the prognostic value of PD‐L1 in breast cancer. We searched Pubmed, Embase, and Cochrane Central Register of Controlled Trials databases for relevant studies evaluating PD‐L1 expression and breast cancer survival. Fixed‐ and random‐effect meta‐analyses were conducted based on heterogeneity of included studies. Publication bias was evaluated by funnel plot and Begg's test. Overall, nine relevant studies with 8583 patients were included. PD‐L1 overexpression was found in 25.8% of breast cancer patients. PD‐L1 (+) associated with several high‐risk prognostic indicators, such as ductal cancer (p = 0.037), high tumor grade (p = 0.000), ER negativity (p = 0.000), PR negativity (p = 0.000), HER2 positivity (p = 0.001) and aggressive molecular subtypes (HER2‐rich and Basal‐like p = 0.000). PD‐L1 overexpression had no significant impact on metastasis‐free survival (HR 0.924, 95% CI = 0.747–1.141, p = 0.462), disease‐free survival (HR 1.122, 95% CI = 0.878–1.434, p = 0.357) and overall specific survival (HR 0.837, 95% CI = 0.640–1.093, p = 0.191), but significantly correlated with shortened overall survival (HR 1.573, 95% CI = 1.010–2.451, p = 0.045). PD‐L1 overexpression in breast cancer associates with multiple clinicopathological parameters that indicated poor outcome, and may increase the risk for mortality. Further standardization of PD‐L1 assessment assay and well‐controlled clinical trials are warranted to clarify its prognostic and therapeutic value.