PDCD1 and neoplasm: PD-1/PD-L1 immune checkpoint inhibitors (ICIs), by binding to PD-1 or PD-L1, block the binding of PD-L1 on the surface of tumor cells and PD-1 on the surface of immune cells, as shown in Figure 1, to relieve the inhibitory effect of tumor cells on the immune system and restore killing effect of the immune system on tumor cells (35, 36).