PDCD1 and gastric cancer: In particular, immune checkpoint inhibitors, such as programmed cell death protein-1 (PD-1) and cytotoxic T lymphocyte-associated protein-4 (CTLA-4) blockade are the focus of tumor therapy [1], which have shown outstanding efficacy in non-small cell lung cancer (NSCLC) [2], gastric cancer [3], and a series of clinical trials in different tumors are ongoing.