PD-L1 Expression in Advanced NSCLC: Insights into Risk Stratification and Treatment Selection from a Systematic Literature Review

Tumors can evade immune detection by exploiting inhibitory immune checkpoints such as the programmed cell death-1 (PD-1)/programmed cell death ligand-1 (PD-L1) pathway. Antibodies that block this pathway offer a promising new approach to treatment in advanced/metastatic non-small cell lung cancer (NSCLC). A systematic review of the literature was conducted to assess the association of PD-L1 with important patient and disease characteristics, the prognostic significance of PD-L1 expressing NSCLC tumors, and the value of PD-L1 as a predictive biomarker of response to anti-PD-1/PD-L1 treatments in advanced/metastatic NSCLC. A total of 35 eligible studies were selected for analysis. Methods used to determine PD-L1 in NSCLC tissue varied considerably; with different PD-L1 antibodies, antibody detection methods, and staining cut-offs. Immunohistochemistry was the most frequent type of PD-L1 assay. Overall, study evidence did not support an association between PD-L1 expression and gender, age, smoking history, tumor histology (adenocarcinoma vs. squamous cell carcinoma), performance status, pathologic tumor grade or EGFR/KRAS/ALK mutational status. In several studies, high PD-L1 expression was associated with shorter survival compared with low expression. Most evidence indicated that patients with high vs. low PD-L1 expression were more likely to experience treatment benefit with anti-PD-1/PD-L1 agents (nivolumab, pembrolizumab, durvalumab, atezolizumab, and avelumab) in advanced NSCLC. Variability in the methods used to determine PD-L1 expression in NSCLC tissue suggests a need for standardized use of well-validated PD-L1 diagnostic assays. Although considerable research links PD-L1 expression in tumors to shorter survival in advanced/metastatic NSCLC, its use as a prognostic factor requires more study. As studies of anti-PD-1/PD-L1 agents continue, PD-L1 is likely to play an important role as a predictive biomarker for selecting patients deriving most benefit from anti-PD-1/PD-L1 monotherapy and directing patients with lower levels of tumor PD-L1 expression (with a high unmet medical need), to alternative treatments, such as combination immunotherapies.