OBJECTIVE: Triple-negative breast cancer (TNBC), a complex and highly aggressive subtype of breast cancer, generally has the poorest clinical outcome, there is a pressing need for more effective therapeutic strategies. Immune checkpoint inhibitors against programmed death 1/programmed death ligand 1 (PD1/PDL1) have revolutionized treatment of several solid tumours, such as non-small cell lung carcinoma (NSCLC), renal, malignant melanoma. However, no checkpoint inhibitors were previously approved for the treatment of TNBC. So far, very limited data have reported PDL1 (SP142) expression and its relationship with clinicopathological behaviors and survival in TNBC. METHODS: PD-L1(SP142) immunohistochemistry was performed on 223 TNBC cases and assessed in tumour cells(TC) as well as tumor-infiltrating lymphocytes(TILs).The relationships between PD-L1 expression and clinicopathological characteristic both in TC and TILs. Futhermore,we also explored the effect of PD-L1 expression on prognosis as illustrated by overall survival(OS). RESULTS: PD-L1 expression was detected in both tumor cells and TILs at a ratio of 8.5 % and 25.1 % respectively. PD-L1 expression in TILs was related to histological grade and abundance of TILs. Tumor cell expression of PD-L1 was not associated with outcome. While PD-L1 expression in TILs and lymphnode transfer were associated with a poor outcome, and PD-L1 expression was an independently prognostic of overall survival (OS) (HR = 0.867, P = 0.029). CONCLUSION: PD-L1 expression in TILs, but not in tumor cells, was a poor prognostic factor in TNBC. These data provide further impetus for assessing immunotherapy in TNBC, in view of the clinical significance of the expression of PD-L1 (SP142) in TNBC.