PDCD1 and nasopharyngeal carcinoma: Indeed, PD-1 and PD-L1 are expressed in many EBV-positive cancers, such as HL, PTLD, DLBCL, NPC, GC, and NKTCL, as well as chronic active Epstein–Barr virus infection (CAEBV), and in infiltrating immune cells [31,32,33,34,35,36,37,38,39,40,41].