Clinicopathological and prognostic significance of PD-L1 in oral cancer: A preliminary retrospective immunohistochemistry study.

OBJECTIVE: To evaluate the relation between PD-L1 expression in oral cavity squamous cell carcinomas and clinicopathological features as well as survival outcomes. METHODS: A retrospective immunohistochemical study was carried out on 55 archived tumours from 55 patients. Tumours were stained for PD-L1 and scored by the proportion of tumour cells with positive membranous staining. PD-L1 scores were compared to the patient's clinicopathological characteristics for any significant associations. Kaplan-Meier curves were constructed for PD-L1 positive and negative tumours to investigate any advantage to survival. RESULTS: Positive PD-L1 staining was found in 58% of tumours and was significantly more likely in non-smokers, non-drinkers and in tongue squamous cell carcinomas. Increased PD-L1 was also associated with increased lymphocyte infiltration as well as PD-L1 staining in lymphocytes and the epithelium adjacent to tumour invasion. No survival benefit was seen from PD-L1 expression in tumour cells. CONCLUSIONS: PD-L1 expression is more common in non-smokers and non-drinkers, and its presence in the adjacent non-tumour epithelium suggests it may be involved in early oncogenesis.