PDCD1 and cancer: Currently, cancer immunotherapies approved by Food and Drug Administration (FDA) roughly included interferon, interleukin-2, dendritic cell vaccine, chimeric antigen receptor-T cells, anti-cytotoxic T lymphocyte antigen-4, anti-programmed cell death protein 1 (PD-1)/PD-L1 monoclonal antibodies, and so on [12].