Background and Objectives: The immune checkpoint ligand programmed death ligand-1 (PD-L1) is expressed in various carcinomas and allows carcinoma cells to elude the immune system. PD-L1 expression is associated with the response to anti-programmed death 1 (PD-1)/PD-L1 drugs. This study aimed to clarify the relationship between PD-L1 expression and clinicopathological factors of salivary gland carcinomas (SGCs) and identify its clinical significance. Methods: PD-L1 expression was examined by immunohistochemical analysis using a tissue microarray comprised of 219 surgically resected SGC specimens. Detailed clinicopathological factors, including patient outcome, were available for all cases. Results: A case showing complete membranous expression of PD-L1 in more than 1% of whole carcinoma cells was considered positive by ROC analysis. A total of 50 (22.8%) patients showed PD-L1 expression in SGC cells. Positive PD-L1 expression was significantly associated with poor disease free survival (P < 0.001) and overall survival (P < 0.001). Multivariate analysis revealed that positive PD-L1 expression was one of the independent predictors for poor disease free survival (hazard ratio = 2.287, 95% confidence interval = 1.24–4.15; P = 0.008). Conclusions: Positive PD-L1 expression was significantly associated with poor disease free survival of SGCs, suggesting that antibody therapies targeting PD-1/PD-L1 may have potential application in SGCs. J. Surg. Oncol. 2016;114:36–43.
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