PD-L1 expression in breast cancer: expression in subtypes and prognostic significance: a systematic review
To systematically review the literature on the expression of PD-L1 in primary BC, variation of expression between subtypes and effect on overall survival (OS), disease-free survival (DFS), and recurrence-free survival (RFS). Additionally, for studies in the neoadjuvant setting, we have reviewed the ability of PD-L1 to predict pathological complete response (pCR).
Articles included in this review were retrieved by searching PubMed (1966–2018) and EMBASE (1980–2018). The following search terms were used: “PD-L1 expression” and “breast cancer” (PubMed234; EMBASE 161).
Thirty-seven articles were found relevant to this study. We summarize important findings from these works, and show that the observed PD-L1 expression in the studies varies greatly, with expression rates ranging from 0 to 83% across subtypes. PD-L1 expression in relation to prognosis both in the adjuvant and neoadjuvant chemotherapy setting remains controversial, with studies finding better, worse, or no effect on prognosis. We also show that a wide variety of strategies are used when evaluating PD-L1 immunohistochemically, e.g., different cut-off points, different cell types evaluated, and different perceptions of when a cell is positive for PD-L1 (cytoplasmic vs membrane staining).
Further investigation of PD-L1 expression in breast cancer and its effect on prognosis is required. There is little consensus on the methods used to evaluate PD-L1 expression immunohistochemically, and this may contribute to the diverging results found in this study.
KeywordsBreast cancer PD-L1 Biomarker Prognostic Immunohistochemistry
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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