PDCD1 and cancer: These inhibitory immune checkpoints usually function as a brake to prevent T cell death, reduce damage in healthy tissue and maintain self-tolerance and homeostasis [2], while in cancer, these checkpoints contribute to the ability of cancer cells to evade immune destruction, which is often cited as a “hallmark of cancer,” providing therapeutic targets for rapidly developing immune-oncological drugs, such as immune-activating PD-1 monoclonal antibodies [3].