The prevalence and prognostic relevance of PD-L1 expression in patients with HPV-negative and HPV-positive oropharyngeal cancer.

Abstract

Background: Human papillomavirus (HPV) associated oropharyngeal squamous cell carcinoma of head and neck is an immunosuppressive malignancy. In head and neck squamous cell carcinoma (HNSCC), various mechanisms have been proposed for the immune escape including immune checkpoint receptors such as PD-1/PD-L1. In this study, we investigated the expression of PD-L1 in HPV-negative and HPV-positive oropharyngeal cancer to determine its prevalence and prognostic relevance. Methods: The expression of PD-L1 was evaluated by immunohistochemistry in 135 specimens of oropharyngeal cancer. A minimum of 20 % tumor cells stained considered positive for PD-L1 expression.HPV-positive tumor was defined as a tumor for which p16 expression was stained in 70 % or more of the tumor cells. Results: The median age of patients was 57 years (range: 35-80), and most of patients were male (90.4 %). Ever smokers were account for 62 % of patients, and most common site of primary tumor was tonsil(78 %). Patient had received CCRT (72 %) or curative surgical resection (28 %). PD-L1 expression was noted in 92 of the 135 patients (68 %). A total of 91 (67 %) patients were positive for p16 expression by immunohistochemistry. There was no significant difference in PD-L1 expression between HPV(-) and HPV(+) tumor (61.4 % vs 71.4 %, p= 0.239). There was no statistically significant difference in the distribution of gender, age, subtype of oropharyngeal cancer, or smoking according to PD-L1 status. With median 43.6 months follow-up, older age (p= 0.070) and T4 stage (p= 0.041) was associated with poor overall survival, while PD-L1 expression was not associated with patients outcome (p = 0.827). Conclusions: PD-L1 expression was found in majority of oropharyngeal cancer patients regardless of HPV status. Further clinical studies with immune checkpoint inhibitors should be warranted both in HPV(-) and HPV(+) oropharyngeal cancer.