Association between PD-L1 expression and head and neck cancer prognosis: a meta-analysis

Background: Programmed cell death ligand 1（PD-L1) plays an important role in tumor cell immune escape, and it has been extensively studied in head and neck cancer. However, its prognostic impact on patients with head and neck cancer remains controversial, so we sought to investigate this issue through a comprehensive meta-analysis. Methods: To assess the significance of PD-L1 on the survival of patients with head and neck cancer, we collected articles reported in PubMed, EMBASE, and Cochrane Library, until January 31, 2019. We also used the Newcastle Ottawa Scale (NOS) for literature quality evaluation. Results: The study included a total of 4551 patients affected by 6 different types of head and neck cancer reported in 26 articles. Our study found that the association between the expression of PD-L1 and the prognosis of head and neck tumors was highly heterogeneous (P < 0.00001, I2 = 80.0%); therefore, the random effects model was applied to combine the effect sizes. Based on the combined hazard ratios (HR)of 1.15 (95% CI: 0.88 to 1.50, P = 0.32), the expression of PD-L1 in head and neck tumors may not be a factor associated with poor prognosis. Conclusions: Our results suggest that PD-L1 expression cannot predict the overall survival of patients with oral, nasopharyngeal, or esophageal cancer. Through subgroup analysis, we found that the expression of PD-L1 may be a poor prognostic factor for some head and neck cancers.