Carcinoembryonic antigen is an embryonic-derived tumor marker that can be expressed by CEA in many gastrointestinal tract tumors and other tumors, such as colorectal cancer, gastric cancer, and lung cancer. Generally speaking, carcinoembryonic antigen CEA is elevated prior to gastric cancer surgery. After surgery, CEA is restored to normal, and when CEA is elevated again in the reexamination, it often indicates the recurrence or metastasis of gastric cancer; if CEA is not elevated before surgery, but is elevated after surgery, after excluding the recurrence or metastasis of gastric cancer, it is considered to be a tumor arising from other parts.