The different role of PD-L1 in head and neck squamous cell carcinomas: A meta-analysis

Programmed cell death-ligands 1 (PD-L1) is a promising immune target for tumor immunotherapy. We conducted this meta-analysis to investigate association between PD-L1 expression and clinicopathological characteristics of head and neck squamous cell carcinomas (HNSCC). Electronic databases were searched for eligible studies. Hazard ratio (HR) with 95 % confidence interval (CI) were extracted to assess the relationship between PD-L1 expression and overall survival (OS) and disease-free survival (DFS) of patients. Odds ratio (OR) with 95 %CI were applied to assess the association between PD-L1 expression and clinicopathological features. A total of 1729 patients were identified for this meta-analysis. PD-L1 expression was higher in female patients in HNSCC (OR = 0.58, 95 %CI:0.44-0.76). In oral squamous cell carcinoma (OSCC), female(OR = 0.56, 95 %CI: 0.41-0.77)and lower grade(OR = 0.48, 95 %CI: 0.24-0.93)were associated with the higher PD-L1 level. There was no significant association between OS and PD-L1 in OSCC patients (HR = 0.89, 95 %CI: 0.37-2.14). In oropharyngeal squamous cell carcinoma (OPSCC), PD-L1 was overexpressed in younger patients (OR = 0.43, 95 %CI: 0.21-0.86), higher tumor grade (OR = 2.46, 95 %CI: 1.38-4.37)and positive HPV status (OR = 2.09, 95 %CI:1.42-3.07). No significant correlation was detected between PD-L1 expression and OS in OPSCC patients (HR = 0.78, 95 %CI: 0.57-1.06). However, the higher PD-L1 expression in tumor cells indicated a better DFS of OPSCC (HR = 0.34, 95 %CI: 0.18-0.67). This meta-analysis demonstrated that PD-L1 overexpression in HNSCC associated with female patients. However, no significant difference was observed in OS or DFS, except the DFS in OPSCC.