In our daily life, any major diseases are caused by not treating small diseases in time, neglecting our health condition, not checking our body regularly, taking medicine indiscriminately when we are sick, not taking medicine according to doctors’ requirements, etc. Stomach is an important organ directly in charge of our digestive and absorption system, how is stomach cancer formed and in what aspects will it be caused by inattention? 1. Environmental factors. The obvious difference of incidence rate between countries and regions indicates that it is related to environmental factors. One of the most important factors in the development of stomach cancer is dietary factors. Salt may be one of the triggering factors of exogenous gastric cancer, and the incidence of gastric cancer is also high in countries with high salt intake. Nitrosamines have successfully induced gastric cancer in animals. Moldy food contains more fungal toxins; rice is processed and covered with talcum powder, whose chemical properties and structure are similar to asbestos fiber, and all the above substances are considered to have carcinogenic effects. Cured meat, smoked fish, spicy hot food, cured meat, smoked fish and other processed meat products contain a large amount of nitrite, which can easily form nitrosamines, which directly induce tumors in the stomach, which is also the reason for the high incidence of gastric cancer in coastal areas, and the high incidence of gastric cancer in the Japanese. Swedish scientists found that for every 30 grams of processed meat products consumed daily, the chances of developing stomach cancer increased by 15%-38%. Stomach cancer is caused by the presence of H. pylori in the stomach. H. pylori, in 1994, was classified by the International Agency for Research on Cancer precisely as ‘a factor that does cause cancer’. 2.Immune factor. The incidence of gastric cancer is higher in people with low immune function. It is possible that the immune dysfunction of the body and the decrease of immune supervision against cancer have some significance in the occurrence of gastric cancer. 3.Precancerous changes. Pre-cancerous changes refer to certain lesions with strong tendency of malignant transformation, which may develop into gastric cancer if not treated. Most of the early gastric cancers are asymptomatic and are usually found by chance during X-ray imaging or endoscopy for reasons such as pain in upper abdomen, abdominal distension and loss of appetite. 4.Diagnostic barium meal of gastric cancer. The double imaging method of stomach was developed in Japan, which has made great contribution to the diagnostic science of gastric cancer. However, with the spread of electronic detection range and the development of endoscopic refinement nowadays, endoscopy that can take tissue has become mainstream. The final diagnosis of benign-malignant is made by the tissue removed by endoscopy (biopsy), and the pathologist makes the final diagnosis. In terms of pathology, gastric cancer is classified as a differentiated adenocarcinoma similar to most normal gastric mucosal structures. However, the pathological diagnosis is benign-malignant, and this alone does not determine the stage of the disease (progression of the cancer). The treatment of cancer, not only gastric cancer, is determined by the stage of the disease. The classification of stage is based on the depth and spread of the cancer and is divided into stages I to IV. Stage I is divided into IA and IB depending on the depth and whether lymph node metastasis is present, and stage III is divided into subcategories IIIA and IIIB. To determine the depth of cancer, endoscopic visualization plus ultrasound endoscopy was used to determine whether the cancer had spread to the outside of the stomach (lymph node metastasis, metastasis to other organs) using CT. Tumor markers, CEA and CA19-9 are used for gastric cancer, and not all of them are positive, and in addition may not be effective for early diagnosis, mainly for prediction of cancer recurrence and for ongoing observation after cancer surgery. If upper abdominal symptoms persist, it is recommended to undergo endoscopy. Upper abdominal symptoms caused by gastric cancer are different from those caused by ulcers and occur with or without food. Even without symptoms, if you are over 40 years old, it is important to undergo regular endoscopy or X-ray for early detection and treatment. The 5-year survival rate for early detection without conscious symptoms is 97%, and now gastric cancer is a completely curable disease if detected early. Stomach cancer is mainly prevented by improving dietary habits and taking care of a reasonable and balanced diet.