CD274 and Epstein-Barr virus infection: To confirm the relationship between EBV infection and PD-L1 expression, we examined PD-L1 expression in 82 NPC samples (42 EBV-positive and 40 EBV-negative cases) and 31 non-tumor nasopharyngeal epithelium (NPE) clinical tissues by performing quantitative real-time PCR (qRT-PCR).