PDCD1 and nasopharyngeal carcinoma: Since the prognostic value of PD-L1 or PD-1 expression in nasopharyngeal carcinoma remains unclear, the aim of the present study was to incorporate all available data using the method of meta-analysis to explore whether different expression status of PD-L1 or PD-1 in patients suffering for nasopharyngeal carcinoma have an effect on their survivals.