PDCD1 and neoplasm: Gao et al. reported that the positive rate of PD-1 on CD8+ T cells was significantly higher in primary tumors and metastatic lymph nodes than that in tumor-free lymph nodes, and that the intensity of PD-1 expression on CD8+ T cells in primary tumors and in metastatic lymph nodes were stronger than that in tumor-free lymph nodes from the same patient [35].