Prognostic significance of circulating exosomal PD-L1 in various malignant tumors: A systematic review and meta-analysis

Although the prognostic significance of exosomal PD-L1 (exoPD-L1) has been previously reported, its value is still controversial. For the first time, we conducted a meta-analysis to systematically evaluate the prognostic value of exoPD-L1 in various types of cancer. The pooled hazard ratio (HR) and 95% confidence interval (CI) in these studies were used to explore the relationship between these indexes and overall survival (OS), recurrence-free survival (RFS), and progression-free survival (PFS). Utilizing the NewcastleLJOttawa Scale (NOS), the quality of the listed studies was assessed. Heterogeneity was explored by subgroup analyses. Beggs and Eggers tests assessed publication bias. This meta-analysis included 11 trials involving 964 cancer cases. The pooled results indicate that high-level pre-treatment exoPD-L1 in circulation was associated with worse OS (HR = 2.10, 95% CI 1.51-2.91, P < 0.001), RFS (HR = 1.67, 95% CI 1.18-2.37, P < 0.01) and PFS (HR = 3.49, 95% CI 2.60-4.68, P < 0.001) compared to those with low-level pre-treatment exoPD-L1. However, high fold changes in circulating exoPD-L1 after receiving immune checkpoint inhibitors (ICIs) were correlated with significantly superior OS (HR = 0.19, 95% CI 0.10-0.38, P < 0.001) and PFS (HR = 0.35, 95% CI 0.23-0.52, P < 0.001). Through this meta-analysis, we found that pre-treatment with high levels of exoPD-L1 is associated with a poor prognosis. However, a high fold change in circulating exoPD-L1 following immunotherapy was correlated with a superior prognosis. ExoPD-L1 may have important clinical significance for assessing the prognosis of cancer patients.