PDCD1 and gastric cancer: Although immune checkpoint blockade with antibodies targeting cytotoxic CTLA-4, PD-1, and PD-L1 has shown clinical activity in some GC patients, it is still unclear which GC subpopulation would benefit most from checkpoint inhibitors (Magalhaes et al., 2018), since PD-L1 immunohistochemistry and tumor mutational burden remain inadequate indicators for guiding treatment (Pagni et al., 2019).