PDCD1 and neoplasm: For the application of immune checkpoint inhibitors, such as PD-1 inhibitors, their anti-tumor activity has been demonstrated, with the reported ORRs of 20.5–34% in pretreated RM-NPC patients [12–15], but it should be noted that the efficacy was also influenced by the expression of programmed cell death-ligand 1 (PD-L1).