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Clin Cancer Res. 2019 Jun 21. doi: 10.1158/1078-0432.CCR-19-1131. [Epub ahead of print]

Prognostic Implications of PD-L1 Expression in Breast Cancer: Systematic Review and Meta-analysis of Immunohistochemistry and Pooled Analysis of Transcriptomic Data.

Author information

1
Breast Center, Theme Cancer, Karolinska University Hospital, Stockholm, Sweden. alexios.matikas@ki.se.
2
Department of Oncology/Pathology, Karolinska Institutet, Stockholm, Sweden.
3
Institute Jules Bordet, Brussels, Belgium.
4
Breast Center, Theme Cancer, Karolinska University Hospital, Stockholm, Sweden.
5
Department of Oncology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
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Contributed equally

Abstract

Purpose: Conflicting data have been reported on the prognostic value of PD-L1 protein and gene expression in breast cancer.Experimental Design: Medline, Embase, Cochrane Library, and Web of Science Core Collection were searched, and data were extracted independently by two researchers. Outcomes included pooled PD-L1 protein positivity in tumor cells, immune cells, or both, per subtype and per antibody used, and its prognostic value for disease-free and overall survival. A pooled gene expression analysis of 39 publicly available transcriptomic datasets was also performed.Results: Of the initial 4,184 entries, 38 retrospective studies fulfilled the predefined inclusion criteria. The overall pooled PD-L1 protein positivity rate was 24% (95% CI, 15%-33%) in tumor cells and 33% (95% CI, 14%- 56%) in immune cells. PD-L1 protein expression in tumor cells was prognostic for shorter overall survival (HR, 1.63; 95% CI, 1.07-2.46; P = 0.02); there was significant heterogeneity (I2 = 80%, P heterogeneity < 0.001). In addition, higher PD-L1 gene expression predicted better survival in multivariate analysis in the entire population (HR, 0.82; 95% CI, 0.74-0.90; P < 0.001 for OS) and in basal-like tumors (HR, 0.64; 95% CI, 0.52-0.80; P < 0.001 for OS; P interaction 0.005).Conclusions: The largest to our knowledge meta-analysis on the subject informs on PD-L1 protein positivity rates and its prognostic value in breast cancer. Standardization is needed prior to routine implementation. PD-L1 gene expression is a promising prognostic factor, especially in basal-like breast cancer. Discrepant prognostic information might be related to PD-L1 gene expression in the stroma.

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