Prognostic significance of programmed cell death ligand 1 expression in patients with ovarian carcinoma A systematic review and meta-analysis

Background: Programmed cell death ligand 1 (PD-L1) overexpression has been reported to be associated with poor prognosis in several human cancers. However, studies on the prognostic value of PD-L1 expression in ovarian carcinoma (OC) remain controversial. This meta-analysis aimed to evaluate comprehensively the prognostic value of PD-L1 in OC. Methods: Electronic databases, including PubMed, EMBASE, and the Cochrane Library, were searched up until March 28, 2018. Hazard ratio (HR), along with 95% confidence interval (CI), was used to analyze the included outcomes. Results: A total of 10 studies with 1179 OC patients were included in this meta-analysis. There was no significant correlation between PD-L1 expression and overall survival (OS) (HR 1.23, 95% CI 0.85-1.79) and progression-free survival (PFS) (HR 0.88, 95% CI 0.52-1.47) of OC patients. However, the subgroup analysis suggested that positive PD-L1 expression was significantly associated with poor OS (HR 1.66, 95% CI 1.08-2.55) and PFS (HR 2.17, 95% CI 1.31-3.61) among OC patients from Asian countries. Increased PD-L1 expression was also a favorable factor for OS (HR 0.73, 95% CI 0.53-0.99) and PFS (HR 0.58, 95% CI 0.45-0.75) in OC patients from non-Asian regions. No evidence of publication bias was detected by the Egger linear regression test and Begg funnel plot. Sensitivity analyses suggested that the results of this meta-analysis were robust. Conclusions: The results indicated that PD-L1 expression may be a negative predictor for prognosis of OC patients from Asian countries, and a good predictor for favorable prognosis of OC patients from non-Asian countries. PD-L1 expression has potential to be a prognostic biomarker to guide clinicians for the selection of individuals who may get clinical benefit from anti-PD-1/PD-L1 immunotherapy. Prospective clinical studies are needed to support these findings.