To investigate the expression of programmed death ligand 1(PD-L1) in triple negative breast cancer (TNBC) and its relationship with PTEN expression.

In the Cancer Genome Atlas (TCGA) database, the expression of PD-L1 mRNA in the invasive breast cancer dataset was analyzed, including 115 TNBC cases and 702 non-TNBC cases. A total of 182 paraffin-embedded tissue specimens from invasive breast cancer patients admitted to the No.180 Hospital of PLA from January 2012 to December 2016 were collected and the expression of PD-L1 and PTEN was immunohistochemically detected. PD-L1 mRNA expression was compared between two groups in TCGA database using t test. χ² test was used to compare the rates. The intensity of PD-L1 positive expression in paraffin-embedded specimens were compared between two groups using Mann-Whitney U test. χ² test and Spearman rank test were used to analyze the correlation between PD-L1 and PTEN expression.

In TCGA database, PD-L1 mRNA level was up-regulated in 3.8% (31/817) of invasive breast cancer. The up-regulation rate of PD-L1 mRNA in TNBC (8.7%, 10/115) was significantly higher than that in non-TNBC (3.0%, 21/702) (χ²=7.314, P=0.007). PD-L1 mRNA expression in TNBC was significantly higher than that in non-TNBC(8.05±0.91 vs 7.38±0.73, t=7.510, P<0.001). The immunohistological results of 182 paraffin-embedded tissue specimens showed that the positive expression rate of PD-L1 in TNBC (14.5%, 9/62) was significantly higher than that in non-TNBC(5.0%, 6/120)(χ²=4.895, P=0.027), and the expression intensity of PD-L1 in TNBC was significantly higher than that in non-TNBC(Z=-2.291, P=0.022). The PD-L1 protein expression was negatively correlated with PTEN protein expression in paraffin-embedded TNBC specimens (χ²=6.913, P=0.009, r=-0.382, P=0.002).

PD-L1, which shows higher expression in TNBC patients than in non-TNBC patients and a negative correlation with PTEN, may be a potential target for TNBC immunotherapy.