Heterogeneity of PD-L1 expression in primary tumors and paired lymph node metastases of triple negative breast cancer

BACKGROUND: Programmed cell death ligand 1 (PD-L1) is a potential predictive biomarker of the response to anti-PD-L1/anti- programmed cell death 1 (PD-1) therapy in multiple cancers, including triple negative breast cancer(TNBC). The purpose of this study was to investigate whether PD-L1 expression is homogenous in primary tumors(PTs) and synchronous axillary lymph node metastases(LNMs) of TNBC. METHODS: PD-L1 expression was immunohistochemically evaluated in 101 TNBC patients’ PTs and paired LNMs. PD-L1 expression in tumor cells and infiltrating immune cells or node lymphocytes in the PTs and associated LNMs was scored separately and was correlated with patients’ clinical parameters and prognoses. RESULTS: PD-L1 expression exhibited spatial heterogeneity in both the tumor cells and the infiltrating immune cells or node lymphocytes of PTs and LNMs. The PD-L1 expression levels were significantly higher in the lymphocytes and tumor cells of the LNMs than in the PTs. PD-L1 expression was also more frequent among the LNMs. PD-L1 expression was associated with high grade and more stromal tumor-infiltrating lymphocytes(TILs). Furthermore, the disease-free survival and overall survival were similar between the PT- negative/LNM- positive and PT- positive/LNM- positive patients, both of which exhibited worse disease-free survival(DFS) thanPT -negative/LNM -negative patients. CONCLUSIONS: The differential expression of PD-L1 between the PTs and LNMs suggests that LNMs PD-L1 status may be used to indicate whether PD-1/PD-L1-targeted therapy would be suitable for a node-positive TNBC patient in the future. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12885-017-3916-y) contains supplementary material, which is available to authorized users.