CD274 and cancer: Expression of PD-L1 in cancer cells binds to programmed death receptor-1 (PD-1) in cytotoxic T cells to inhibit proliferation, migration, and secretion of cytotoxic substances, so as to impair the activity of cytotoxic T cells and thus prevent the tumor cells from being killed (Herbst et al., 2014; Kim and Chen, 2016).