I. Overview Gastric cancer is one of the most common malignant tumors in China. 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, and the progressive gastric cancer still accounts for 80G-90G. The occurrence of gastric cancer is the result of the long-term role 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. Studies have shown that Helicobacter pylori (H. pylori) infection, diet, smoking and host genetic susceptibility are important factors affecting the occurrence of gastric cancer. In order to further standardize gastric cancer diagnosis and treatment, improve the level of gastric cancer diagnosis and treatment, improve the prognosis of gastric cancer patients, guarantee medical quality and medical safety, and develop the discipline in the future, this standard is formulated. Diagnosis The diagnosis and differential diagnosis of gastric cancer should be made by combining clinical manifestations, endoscopy, histopathology and imaging examination of patients. (I) Clinical manifestations. Gastric cancer lacks specific clinical symptoms, and early gastric cancer is often asymptomatic. The common clinical symptoms include discomfort or pain in the upper abdomen, loss of appetite, emaciation, weakness, nausea, vomiting, vomiting blood or black stool, diarrhea, constipation, fever, etc. (B) Physical signs. Early stage or part of locally progressive gastric cancer often has no obvious physical signs. Patients with advanced gastric cancer may find upper abdominal masses, and when distant metastasis occurs, corresponding signs may appear according to the metastatic site. When upper gastrointestinal perforation, bleeding or gastrointestinal obstruction occurs, corresponding signs may appear. (C) Ancillary examinations. 1.Endoscopic examination. (1) Gastroscopy: It is a necessary examination means to confirm the diagnosis of gastric cancer, which can determine the location of tumor and obtain tissue specimens for pathological examination. If necessary, pigmented endoscopy or magnification endoscopy can be used as appropriate. (2) 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 surgery such as endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD). (3) Laparoscopy: Laparoscopy may be considered for those who suspect peritoneal metastasis or intra-abdominal dissemination. The development of laparoscopic ultrasonography has led to more accurate preoperative staging.