A number of clinical studies point to the following as markers of great importance for the diagnostics and functioning of GC: human epidermal growth factor receptor 2 (HER2), carcinoembryonic antigen (CEA), mucin 1 (MUC1), epithelial cell adhesion molecule (EpCAM), claudin 18.2 (CLDN 18.2), mesothelin (MSLN), natural-killer receptor group 2, member D (NKG2D), and folate receptor 1 (FOLR1). The gene discussed is CEACAM5; the disease is gastric cancer.