Objective To systematically evaluate the prognostic and clinicopathological significance of PD-L1 expression in colorectal cancer(CRC) tissues by meta-analysis.

Methods PubMed, Embase, Web of Science, Cochrane Library, CNKI and Wanfang database were used to search for the studies related to PD-L1 expression and the prognosis of CRC. The search time was until June 2018. The data of survival and clinicopathological features were extracted from eligible studies and analyzed by Stata SE12.0 software.

Results Eighteen studies with 5724 CRC patients were enrolled. PD-L1 expression in CRC tissues was associated with shorter overall survival (OS) (HR:1.40, 95%CI:1.02-1.93, P=0.039) and relapse-free survival (RFS) (HR:1.67, 95%CI:1.27-2.20, P=0.000), but not with disease-free survival (DFS)(P=0.933). And PD-L1 expression was significantly associated with tumor differentiation(P=0.016) and lymph node metastasis(P=0.028), but not with gender, tumor location, TNM staging, invasion depth, venous invasion, chemotherapy, MSI status or KRAS mutation. In addition, subgroup analysis showed that PD-L1 expression in tumor cells, not in tumor infiltrating immune cells (OS: P=0.991; RFS: P=0.210), was significantly associated with shorter OS(P=0.033) and RFS(P=0.001).

Conclusion PD-L1 expression in CRC tissues is associated with poor prognosis. In addition, the prognostic significance of PD-L1 expression in tumor cells might be inconsistent with that in tumor-infiltrating immune cells.