Due to the high target affinity, peptide inhibitors have been developed to disrupt the PD-1/PD-L1 axis, the cGAS-STING pathway, CD47/SIRPα pathway et al., which become a promising complement for cancer immunotherapy, and some of what could penetrate tumor tissue and significantly inhibit tumor growth and metastasis in anti-PD-1 resistant tumor models. Here, PDCD1 is linked to cancer.