Clinicopathological and prognostic significance of programmed cell death ligand 1 (PD-L1) expression in patients with esophageal squamous cell carcinoma: a meta-analysis

Background: The clinicopathological and prognostic significance of programmed cell death ligand 1 (PD-L1) expression in patients with esophageal squamous cell carcinoma (ESCC) remains controversial. To investigate this question, we conducted a meta-analysis. Methods: A comprehensive literature search of electronic databases (up to July 10, 2016) was performed for relevant studies using multiple search strategies. Correlation between PD-L1 expression and clinicopathological features/overall survival (OS) was analyzed. Results: A total of 1,350 ESCC patients from eight studies were included. The pooled odds ratios (ORs) indicated that none of the clinicopathological characteristics was correlated with PD-L1 expression, including gender [OR=0.84; 95% confidence interval (CI): 0.59-1.18; P=0.31], histological differentiation (OR=1.33; 95% CI: 0.95-1.85; P=0.09), tumor depth (OR=0.66; 95% CI: 0.33-1.35; P=0.26), status of lymph node metastasis (OR=0.67; 95% CI: 0.30-1.52; P=0.34), distal metastasis (OR = 0.66; 95% CI: 0.40-1.09; P= 0.10) and tumor node metastasis (TNM) stage (OR=0.93; 95% CI: 0.49-1.75; P=0.82). The combined hazard ratio (HR) for OS showed a trend that overexpression of PD-L1 might be associated with the survival outcome of ESCC, though the difference was not statistically significant (HR = 1.65; 95% CI 0.95-2.85; P=0.07). Conclusions: Based on the published studies, PD-L1 overexpression in ESCC was not associated with common clinicopathological characteristics. PD-L1 might be a poor prognostic biomarker for ESCC. Further large-scale research should be performed to reveal the precise clinicopathological and prognostic significance of PD-L1 in ESCC by unified testing standard.