Purpose: The aim of this study was to elucidate the rates and prognostic roles of programmed cell death ligand 1 (PD-L1) immunohistochemical (IHC) expression in various malignant tumors through a systematic review and meta-analysis.
Method: The current study included 16,176 patients from 97 eligible studies. We investigated PD-L1 expression and its correlation with survival rate in various malignant tumors.
Results: The estimated rate of PD-L1 IHC expression was 0.449 (95% confidence interval [CI] 0.404-0.495). The highest and lowest PD-L1 expression levels were found in thyroid cancer (0.829, 95% CI 0.781-0.868) and small-cell neuroendocrine carcinoma (0.005, 95% CI 0.000-0.080), respectively. PD-L1 expression was significantly correlated with poorer overall survival and disease-free survival rates (hazard ratios 1.276, 95% CI 1.097-1.486 and 1.304, 95% CI 1.034-1.644, respectively). However, PD-L1 IHC expression was significantly correlated with worse overall survival rates in patients with esophageal cancer and renal cell carcinoma and with worse disease-free survival rates in patients with colorectal cancer, hepatocellular carcinoma, and renal cell carcinoma.
Conclusions: Our results show that PD-L1 expression rates and the correlations with survival varied between tumor types. Detailed evaluation criteria for PD-L1 will have to be standardized before application to specific tumor types.