Early gastric cancer patients may have no clinical symptoms or only mild indigestion symptoms, such as epigastric discomfort, slight fullness, loss of appetite, acidity, pain, nausea, belching, etc. These symptoms are not unique to gastric cancer, but can be seen in chronic gastritis, ulcer disease, functional dyspepsia. These symptoms are not unique to gastric cancer, but can be seen in chronic gastritis, ulcer disease and functional dyspepsia. As the disease progresses, symptoms such as unexplained weight loss, weight loss, fatigue and weakness, black stool or upper abdominal masses may appear; pancreatic tumor may start to appear as unpleasant eating and gradually develop into difficulty in swallowing and food reflux; further development of gastric sinus cancer may result in vomiting due to pyloric obstruction. The best method for early diagnosis of gastric cancer is gastroscopy, which can not only visualize various parts of esophagus, stomach and duodenum, but also biopsy the lesion mucosa to clarify the nature of the lesion. At present, gastroscopy plus histopathological examination is the gold standard for gastric cancer diagnosis. The current gastroscopy not only has high clarity, but also can perform narrow spectrum imaging (NBI) and electronic light staining (i-Scan) at the same time of examination, which greatly improves the recognition rate of lesions that are not significant under conventional endoscopy. If necessary and possible, chemical staining of the mucosa (indigo carmine) can be performed under gastroscopy, which facilitates the identification of microscopic lesions. Moreover, with the development of gastroscopy technology, some small superficial gastric cancers can be removed by gastroscopic mucosal resection (EMR) or mucosal dissection (ESD) without the need for major gastrectomy, which greatly reduces the trauma of surgery. For patients with fear of gastroscopy, they can also choose to undergo painless gastroscopy and complete the gastroscopy in their sleep without pain. Pre-cancerous state of the stomach includes: (1) Chronic atrophic gastritis: there is a significant positive correlation between chronic atrophic gastritis and the incidence of gastric cancer. (2) Pernicious anemia: gastric cancer occurs in 10% of patients with pernicious anemia, and the incidence of gastric cancer is 5-10 times that of normal population, which is less common in China. (3) Gastric polyps: Although adenomatous polyps do not account for a high proportion of gastric polyps, the cancer rate is high. The cancer rate is higher for those with diameter greater than 2cm. (4) Stomach remnant: the cancer that occurs in the remnant stomach after surgery for benign gastric lesions is called remnant gastric cancer. The incidence rate increases significantly after gastric surgery, especially from 10 years after surgery. (5) Chronic gastric ulcer: gastric ulcer itself is not a pre-cancerous state. Instead, the mucosa at the edge of the ulcer is prone to intestinal epithelial metaplasia and malignancy. (6) Giant gastric mucosal fold disease (Menetrier’s disease): serum protein is lost through giant gastric mucosal fold, with clinical hypoproteinemia and swelling, and about 10% can become cancerous. Pre-cancerous lesions of the stomach include: (1) heterogeneous hyperplasia: also known as atypical hyperplasia, currently called intraepithelial neoplasia. In particular, moderate to severe atypical hyperplasia (high-grade intraepithelial neoplasia also includes carcinoma in situ) is prone to carcinogenesis. (2) Intestinal metaplasia: Intestinal metaplasia is the necessary basis for the occurrence of gastrointestinal type adenocarcinoma, especially the more extensive moderate to severe intestinal metaplasia is closely related to the occurrence of gastric cancer. Patients with the above conditions should have timely or regular review of gastroscopy. In addition, those who are older than 40 years old and have eaten pickled food for a long time and have H. pylori infection with upper abdominal discomfort symptoms should also undergo gastroscopy promptly. Since the symptoms of gastric cancer lack specificity, patients with symptoms such as upper abdominal discomfort, vague pain in the upper abdomen, feeling of fullness after eating, loss of appetite, emaciation, weakness, vomiting, black stool, etc., especially if these symptoms occur repeatedly for a long period of time, should promptly seek medical attention and undergo gastroscopy. Even for patients younger than 40 years old, because the tendency of younger gastric cancer patients detected in recent years is more obvious, the youngest gastric cancer patient we diagnosed is only 14 years old, and several cases of gastric cancer patients younger than 30 years old are detected every year. Therefore, it is very necessary to conduct self-awareness screening according to one’s own situation when it is not possible to conduct screening for gastric cancer in China at present.