OBJECTIVE Programmed cell death-ligand 1(PD-L1) is the suppressor expressed on the surface of several kinds of tumor cells,which plays an important role in immune escape of malignancies.This study investigated the correlation of PD-L1 expression with clinicopathological features and prognosis in breast cancer through a meta-analysis.METHODS PubMed,EMBASE,Cochrane Library Database,CNKI,Wan Fang and VIP databases were searched for collecting retrospective cohort studies of the association between PD-L1 expression and breast cancer,up to Feb 1st,2018.Literature screening was operated by two researchers through the inclusion/exclusion criteria.Meta analysis was carried out by Review Manager 5.3 software.Newcastle-Ottawa Scale(NOS) was used for evidence quality assessment,and publication bias was evaluated by the Stata 12.0 software.RESULTS Ten studies (involving 2 864 patients) were included in the meta-analysis.Results suggested that PD-L1 positive expression was associated with worse OS (HR=2.10,95%CI:1.19-3.71,P=0.010) and DFS (HR=1.36,95%CI:1.03-1.79,P=0.030).The expression level of PD-L1 in breast cancer and triple negative breast cancer tissues was especially higher than that of control tissues and non-triple negative breast cancer tissues.Moreover,higher PD-L1 expression was related with lymph node metastasis (OR=0.72,95%CI:0.53-0.96,P=0.030),histologic grade (OR=0.55,95%CI:0.40-0.75,P<0.001) and ER expression (OR=3.27,95%CI:1.25-8.55,P=0.020).There was no significant correlation with PR (OR=3.08,95%CI:0.98-9.69, P=0.050) and HER-2 expression (OR=0.87,95%CI:0.59-1.29,P=0.490).CONCLUSION The meta-analysis shows that PD-L1 higher expression is associated with worse survival in breast cancer and is more common in patients with lymph nodes metastasis,higher histologic grade or negative ER expression. © 2018, Editorial Board of Chinese Journal of Cancer Prevention and Treatment. All right reserved.