PDCD1 and gastric cancer: To date, PD1/PDL1 checkpoint blockade therapy is widely performed to various malignancies including GC (Kang et al., 2017; Fuchs et al., 2018; Kim et al., 2018), but some studies discovered that PD-1 has a critical function in tumor antigen tolerance, leading to poor therapeutic effect in some patients with PD1 therapy (Woo et al., 2012; Kang et al., 2017).