I. Overview Gastric cancer is one of the most common malignant tumors in China. The 2010 Health Statistical Yearbook shows that in 2005, the mortality rate of gastric cancer accounted for the 3rd place of malignant tumor mortality in China. The occurrence of gastric cancer is the result of the long-term effect of multiple factors. There are obvious regional differences in the incidence of gastric cancer in China, and environmental factors are dominant in the occurrence of gastric cancer, while host factors are subordinate. Some studies have shown that H. pylori infection, diet, smoking and genetic susceptibility of the host are important factors affecting the occurrence of gastric cancer. Diagnosis The diagnosis and differential diagnosis of gastric cancer should be made by combining clinical manifestations, endoscopy, histopathology and imaging examinations of patients. 1.Clinical manifestations: Gastric cancer lacks specific clinical symptoms, and early gastric cancer is often asymptomatic. The common clinical symptoms include discomfort or pain in upper abdomen, loss of appetite, emaciation, weakness, nausea, vomiting, vomiting blood or black stool, diarrhea, constipation, fever, etc. 2.Signs: Early stage or part of locally progressive gastric cancer often has no obvious signs. In advanced gastric cancer patients, upper abdominal masses can be found, and in case of distant metastasis, corresponding signs can appear according to the metastasis site. In case of upper gastrointestinal perforation, bleeding or gastrointestinal obstruction, corresponding signs may appear. 3.Auxiliary examination: (1) Endoscopy. (2) Gastroscopy: It is a necessary examination to confirm the diagnosis of gastric cancer, to determine the location of tumor and to obtain tissue specimens for pathological examination. If necessary, pigmented endoscopy or magnification endoscopy can be used as appropriate. (3) Ultrasonic gastroscopy: It is helpful to evaluate the depth of gastric cancer infiltration and determine the status of perigastric lymph node metastasis, and is recommended for preoperative staging of gastric cancer. This examination is necessary for those who intend to perform minimally invasive procedures such as endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD). (4) Laparoscopy: laparoscopy can be considered for those who suspect peritoneal metastasis or intra-abdominal dissemination.