The Prognostic Significance of Soluble Programmed Death Ligand 1 Expression in Cancers: A Systematic Review and Meta-analysis

The differential expression of soluble programmed death ligand 1 (sPD-L1) has been found in some cancers; however, the correlation between sPD-L1 expression and prognosis value in tumour is still unclear. Here, we conducted a meta-analysis and systematic review to assess the prognostic value of sPD-L1 in patients with cancer. Eligible studies were searched for in the databases including PubMed, Web of Science, ScienceDirect and Wiley Online Library database. The pooled hazard ratios (HRs) with a 95% confidence interval (95%CI) were calculated to assess the prognostic significance of sPD-L1 in human cancer. Eight studies and 1102 patients with cancer were included in the final analysis, and the combined analysis indicated that a higher level of sPD-L1 was associated with worse overall survival (OS) (HR = 1.60, 95%CI: 1.21-1.99). Furthermore, statistical significance was also observed in subgroup analysis stratified by the cancer type (haematological neoplasms or non-haematological neoplasms), sample size (more or less than 100), cut-off value of sPD-L1 (more or less than 6.51 ng/ml) and ethnicity (Asian or European). The meta-analysis indicates that circulating sPD-L1 changes may serve as a useful biomarker for cancer prognosis, and higher level of sPD-L1 may also be associated with poor outcomes in patients with cancer.