Prevalence of PD-L1 expression in head and neck squamous precancerous lesions: a systematic review and meta-analysis

Background: Studies concerning programmed death-ligand 1 (PD-L1) expression in precancerous lesions of head and neck (HN) region have shown variable results. Methods: We systematically reviewed the published evidence on PD-L1 expression in HN precancerous lesions. Results: Of 1058 original articles, 14 were included in systematic review and 9 in meta-analysis. The pooled estimate of PD-L1 expression was 48.25% (confidence interval [CI] 21.07-75.98, I2 98%, tau2 0.18). PD-L1 expression appeared to be more frequent in precancerous lesions than in normal mucosa (risk ratio [RR] 1.65, CI 0.65-4.03, I2 91%, tau2 0.82) and less frequent than in invasive squamous cell carcinoma (RR 0.68, CI 0.43-1.08, I2 91%, tau2 0.22). Conclusions: PD-L1 expression could reflect a point of balance between host immune response and cancer escape ability. High heterogeneity and moderate quality suggest that further studies with larger sample size and more rigorous case selection will allow more precise assessment of PD-L1 expression in HN precancerous lesions.