PDCD1 and neoplasm: Once PD-1 binds to PD-L1, not only can the PD-1/PD-L1 pathway inhibit the activation and physiological function of T cells, the proliferation of NK cells and the production of B cell antibodies, but can also promote the stability of Treg cells to enhance their inhibitory function, thus leading to immune suppression and tumor immune evasion [1,2].