Results in Figure 2B showed that the positive percentage of PD-1 expression in the primary NPC (25.0%, 6/24) was significantly lower than that in matched metastasis (62.5%, 15/24) (P=0.009), as well as the co-expression of PD-1 and PD-L1 (P=0.009) (Figure 2B). The gene discussed is PDCD1; the disease is nasopharyngeal carcinoma.