PDCD1 and neoplasm: More frequency of CD8+ T cells in the blood represents systematic antitumor immune features, and they could migrate to the tumor site, lymph nodes, and distal sites to enhance antitumor ability (17, 23, 24), which was consistent with the findings from a recent study (12) to investigate the peripheral blood cells to predict response to anti-PD-1 immunotherapy in melanoma.