Most early gastric cancers (EGC) can be treated radically under endoscopy, and the 5-year survival rate is over 90%. Early detection, early diagnosis and early treatment of cancer are the main strategies to reduce mortality and increase survival rate. Therefore, screening and early diagnosis and treatment by endoscopy among high-risk groups of gastric cancer is an efficient and feasible way to change the serious situation of gastric cancer diagnosis and treatment in China. I. Basic concept: Early gastric cancer: In early gastric cancer, the cancerous tissue is only limited to the gastric mucosal layer or submucosal layer, regardless of whether there is lymph node metastasis or not. There are special types of early gastric cancer, micro gastric cancer is early gastric cancer with the maximum diameter of lesion ≤ 5 mm, small gastric cancer is early gastric cancer with the maximum diameter of lesion 5-10 mm. Precancerous condition: It includes two concepts: precancerous discases and precancerous lesions. The former refers to benign gastric diseases associated with gastric cancer, which have the risk of gastric cancer and are clinical concepts, such as chronic atrophic gastritis, gastric ulcer, gastric polyp, postoperative gastric, Menetrier’s disease (hypertrophic gastritis), pernicious anemia, etc. The latter refers to pathological changes that have been proved to be closely related to gastric cancer, i.e., intraepithelial hyperplasia or intraepithelial neoplasia, and is a pathological concept. neoplasia), which is a pathological concept. Intraepithelial neoplasia: Intraepithelial neoplasia is divided into two grades, namely low-grade intraepithelial neoplasia (LGIN) and high-grade intraepithelial neoplasia (HGIN). LGIN is equivalent to mild and moderate heterogeneous hyperplasia, and HGIN is equivalent to severe heterogeneous hyperplasia and carcinoma in situ. Risk factors of gastric cancer 1. Demographic factors: demographic factors such as age and gender are risk factors of gastric cancer. The incidence rate and mortality rate of gastric cancer increase with age. In China, the incidence rate of gastric cancer increases significantly after the age of 40, and then decreases gradually after reaching the peak, and the incidence cases under the age of 30 are rare. A large prospective follow-up study in Japan found that daily salt intake of more than 10 g significantly increased the incidence of gastric cancer, and the association between patients with atrophic gastritis with infection and gastric cancer was more obvious. Pickled, smoked, fried and baked foods. These foods produce carcinogens such as polycyclic aromatic hydrocarbons and N-nitroso compounds, which have been shown to be closely related to gastric cancer in several studies in Iceland, Japan, Uruguay and ethnic minority areas in China. Bad dietary habits. Bad dietary habits can lead to repeated damage and repair of gastric mucosa and reduce the protective effect of gastric mucosa, which can lead to carcinogenesis in the long term. Smoking: Several prospective studies have found a dose-response relationship between smoking and the risk of gastric cancer, with the risk of gastric cancer increasing with the amount and duration of daily smoking and associated with higher recurrence and mortality of gastric cancer. Infectious factors: Meta-analysis has shown that H and pylori infection can increase the risk of gastric cancer by twofold. Although 2 billion people in the world population are infected with H, pylori, less than 1% of the H, pylori-infected population eventually develop gastric cancer, suggesting that H, pylori infection is not a sufficient condition for gastric cancer development, but rather that gastric cancer development is the result of a series of interactions between bacterial virulence factors and the genetic background and environment associated with the host inflammatory response. Whether H and pylori eradication can reduce gastric cancer mortality and effectively reduce atrophy and intestinal epithelial hyperplasia, and whether H and pylori eradication after endoscopic resection of early gastric cancer can prevent heterochronic carcinogenesis are inconsistent and need to be confirmed by further studies. Genetic factors: Epidemiological data suggest that some gastric cancers have a tendency to accumulate in families, among which hereditary diffuse gastric cancer (about 1%-3% of all gastric cancers) is caused by mutations in the CDH1 gene encoding epithelial calreticulin (E-cadherin), and germline mutation carriers have an 80% lifetime probability of developing hereditary infiltrative gastric cancer. Other familial diseases are associated with an increased risk of gastric cancer, such as Lynch syndrome and familial adenomatous polyposis. Other factors: Environmental factors such as geology and drinking water may influence the development of gastric cancer through interaction with genetic background H, pylori infection, host immunity, etc. Psychosocial factors (such as mental stimulation or depression) and immune factors may have some association with gastric cancer occurrence, but whether they are confirmed risk factors needs further study. The knowledge of the population about gastric cancer prevention and treatment is also an important factor influencing early diagnosis and treatment of gastric cancer. Protective factors: Fruit and vegetable intake is a protective factor for gastric cancer. A large-scale prospective study found that the risk of gastric cancer was reduced by 44% in the high intake group compared with the low daily fruit and vegetable intake group. A recent Meta-analysis showed that dietary fiber intake was negatively correlated with gastric cancer risk, and consumption of onion and garlic vegetables could also reduce the occurrence of gastric cancer. Early screening of gastric cancer 1. According to the national conditions and epidemiology of gastric cancer in China, any of the following should be classified as high-risk group of gastric cancer and recommended as screening target: age above 40 years, male or female; people in areas with high incidence of gastric cancer; people with H, pylori infection; people with chronic atrophic gastritis, gastric ulcer, gastric polyp, post-surgical residual stomach, hypertrophic gastritis, pernicious anemia and other pre-cancerous gastric diseases. pre-cancerous diseases such as gastric cancer; first-degree relatives of gastric cancer patients; presence of other high-risk factors for gastric cancer (high salt, pickled diet, smoking, heavy alcohol consumption, etc.). Those who have the following alarm symptoms including gastrointestinal bleeding, difficulty in swallowing, elimination, upper abdominal discomfort, upper abdominal mass, etc. need to pay more attention. Screening methods (1) Endoscopic screening: Endoscopy and endoscopic biopsy are the gold standard for the diagnosis of gastric cancer, especially for flat type and non-ulcerous gastric cancer, and the detection rate is higher than that of barium x-ray. However, endoscopy relies on equipment and endoscopist resources, and is relatively expensive, painful, and poorly accepted by patients, and has not been used for mass gastric cancer screening even in developed countries such as Japan. Endoscopic examination methods include ordinary white light endoscopy, chemical staining endoscopy and electronic staining endoscopy, etc. (2) Biopsy If no suspicious lesion is found after endoscopic observation and special endoscopic techniques such as staining, biopsy may not be taken. If a suspicious lesion is found, biopsy should be taken, and the number of biopsies taken depends on the size of the lesion. Treatment 1. Treatment principles of early gastric cancer include endoscopic resection and surgical operation. Compared with traditional surgery, endoscopic resection has the advantages of less trauma, fewer complications, faster recovery and lower cost, and the efficacy is comparable, and the 5-year survival rate can exceed 90%. Therefore, many international guidelines and this consensus recommend endoscopic resection as the first choice of treatment for early gastric cancer. Endoscopic resection for early gastric cancer mainly includes endoscopic mucosal resection (EMR) and endoscopic submucosal dissection (ESD), and the major difference between the indications of EMR and ESD is that both methods EMR has a size limit for whole lesions and can only remove lesions in the mucosal layer, whereas ESD has no size limit and can remove lesions in the SM1 layer. Compared with EMR, ESD has a higher rate of resection and complete resection of early gastric cancer and a lower rate of local recurrence, but a higher rate of complications such as perforation. ESD definition: ESD is a new technique developed on the basis of EMR. According to the lesions of different sites, sizes and infiltration depths, special electrodes such as IT knife, Dua knife, Hook knife, etc. are selected to gradually separate the tissues between the mucosal layer and intrinsic muscle layer under endoscopy, and finally the diseased mucosa and submucosa are completely peeled off. The indications for endoscopic resection of early gastric cancer in China are as follows: absolute indications: differentiated mucosal carcinoma with a maximum diameter of ≤2 cm and no combined ulcers; HGIN of gastric mucosa; relative indications: differentiated mucosal carcinoma with a maximum diameter of >2 cm and no ulcers; differentiated mucosal carcinoma with a maximum diameter of ≤3 cm and ulcers; undifferentiated mucosal carcinoma with a maximum diameter of ≤2 cm and no ulcers; and endoscopic resection of mucosal carcinoma with a maximum diameter of ≤3 cm and ulcers. In addition to the above conditions, early gastric cancer with poor general condition, contraindication to surgery or refusal to surgery can be considered as relative indications for ESD. Currently, there are more recognized contraindications to endoscopic resection in China: early gastric cancer with clear lymph node metastasis; cancer invading the intrinsic muscular layer; and patients with coagulation dysfunction. In addition, the relative contraindications for ESD include negative lift sign, which means that the submucosal layer at the base of the lesion cannot form a local augmentation after the injection of 0,9% NaCl solution, suggesting that there are adhesions between the submucosal layer and the muscular layer at the base of the lesion; the risk of perforation is higher when ESD treatment is performed at this time, but with the skillful operation of ESD, even if the lift sign is negative, ESD can be performed safely. H, pylori eradication: For H, pylori infection, which is considered a risk factor for ulcer recurrence, it is recommended to eradicate H, pylori after ESD. postoperative eradication of early gastric cancer can even reduce the incidence of heterochronic gastric cancer. V. Postoperative follow-up (monitoring) With regard to postoperative endoscopic follow-up, it is more commonly accepted in China to review gastroscopy once at 3, 6 and 12 months after curative resection, and annually thereafter, together with tumor markers and related imaging. It is recommended that medical units that are in a position to do so conduct studies to review patients with colonoscopy at the same time, as the likelihood of intestinal adenoma is significantly higher in patients with early gastric cancer than in the healthy population.