PDCD1 and gastric cancer: The results revealed that some key immune checkpoint molecules were significantly overexpressed in the high-risk group, such as CTLA4 (Cytotoxic T-lymphocyte associated protein 4), PD-1 (Programmed cell death 1) and corresponding ligand PD-L1(Programmed cell death 1 ligand 1), indicating that high-risk GC tends to be immunosuppressive (Figures 9A–D; Figure S3).