Prognostic and clinicopathological roles of programmed death-ligand 1 (PD-L1) expression in thymic epithelial tumors: A meta-analysis.

BACKGROUND Programmed death-ligand 1 (PD-L1) is one of the immune checkpoint proteins, and plays an important role in the progression and microenvironment of cancer. PD-L1 expression has been associated with poor survival in many cancers. Several studies have also shown an association between PD-L1 expression and the prognosis of patients with thymic epithelial tumors (TETs). In this study, we systematically evaluated the prognostic and clinicopathological roles of PD-L1 expression in TETs. METHODS We searched the literature through PubMed, Embase and Cochrane library and chose the eligible studies, and subsequently performed a meta-analysis to evaluate the prognostic and clinicopathological roles of PD-L1 expression in TETs. RESULTS Six of the 75 articles found in the literature were selected. PD-L1 expression was significantly related to unfavorable overall survival (hazard ratio 1.52, 95% confidence interval [CI]: 1.01-2.30, P = 0.046) in TETs. PD-L1 expression was significantly associated with male gender (odds ratio [OR] 1.55, 95% CI: 1.08-2.22, P = 0.017) and higher Masaoka stage (OR 3.93, 95% CI: 2.44-6.32, P < 0.001). CONCLUSIONS PD-L1 expression was correlated with unfavorable prognosis in TETs, indicating PD-L1 expression could help determine the prognosis of TET patients.