PD-L1 expression and patient outcomes in gastrointestinal neuroendocrine neoplasm: a meta-analysis

Programmed cell death ligand 1 (PD-L1) is a known prognostic and therapeutic marker in malignant tumors. This meta-analysis aimed to investigate the association of PD-L1 expression with the clinicopathological parameters and survival outcomes of gastrointestinal neuroendocrine neoplasms (NENs).

PubMed, EMBASE, Web of Science, OVID Medline, the Cochrane Library, and Google Scholar were searched for relevant studies June 30, 2020. Studies reporting PD-L1 immunohistochemistry of gastrointestinal NEN with associated survival data or clinicopathological parameters were included.

In total, 10 studies were included. Odd ratios (ORs) were combined to evaluate association between PD-L1 expression and clinicopathological parameters. Hazard ratios (HR) and standard errors were combined to evaluate the association between PD-L1 expression and overall survival. PD-L1 expression was significantly associated with higher tumor grade [OR: 3.42; 95% confidence interval (CI): 2.00-5.85, P<0.05] and lymph node metastasis (OR: 1.94; 95% CI: 1.13-3.34, P=0.02). However, PD-L1 expression was not associated with age, sex, and tumor stage. The pooled hazard ratio (HR: 2.45, 95% CI: 1.20-4.98, P<0.05) showed a significant association between PD-L1 expression and shorter overall survival.

The results of this meta-analysis show that PD-L1 expression in tumor cells of gastrointestinal NEN can be used as a biomarker of worse survival and important clinicopathological parameters. Further, it can also be used as a therapeutic biomarker for developing novel treatment modalities that can improve prognosis. Although the results of this meta-analysis are more robust than those of the individual studies analyzed, this study also has several limitations. Further studies with a larger study population and consistent method for evaluating PD-L1 expression are needed to validate our results.