Gastric cancer is a common malignant tumor in China, the cause of which is not fully understood, and it is generally believed that the occurrence of gastric cancer is the result of a combination of multiple factors. The external environment and dietary factors are most closely related to the occurrence of gastric cancer, and there are certain conditions in the human body that are conducive to the occurrence of gastric cancer and should not be ignored. Helicobacter pylori has been identified by the World Health Organization as the first type of gastric cancer carcinogen, and nitrosamines are also possible gastric cancer-causing substances. Nitrosamines are the products of nitrate reduction to nitrite and then combined with amine. Both nitrate and nitrite are widely found in pickles, salted vegetables, salted fish, salted meat and smoked food. Geographical and environmental factors Surveys on the epidemiology of gastric cancer around the world show that there are significant differences in the incidence of gastric cancer among different regions and races. Some data indicate that gastric cancer mostly occurs in high latitudes, and the more distant countries are from the equator, the higher the incidence of gastric cancer. It is also suggested that its incidence is related to coastal factors. Different dietary habits are also considered to be an important factor. Excessive intake of salt, salted foods with high salt content, smoked fish, and foods with nitrosamines are factors associated with the development of stomach cancer, as well as moldy foods with high levels of fungal toxins and rice processed and covered with talcum powder. In addition, there are also studies showing that stomach cancer is related to nutrient imbalance. Some people also believe that geochemical factors and the presence of carcinogens in the environment should also be considered. Genetic Factors Clinical workers have encountered cases where more than two members of a family have stomach cancer, and although this tendency to develop stomach cancer is very rare, it at least suggests the possibility of genetic factors. Some data reported that the incidence of gastric cancer among relatives of patients with gastric cancer is four times higher than that of the control group. Among the genetic factors, many authors have noted the relationship of blood type. Some statistics show that the incidence of gastric cancer is 20% higher in people with type A than in people with other blood types. However, there are some reports that there is no difference in the incidence of gastric cancer among people with different blood types. In recent years, some people have studied the relationship between the incidence of gastric cancer and HLA, and further conclusions have yet to be made. Pre-cancerous changes refer to certain lesions with strong malignant tendency, which may develop into gastric cancer if left untreated. Pre-cancerous changes include pre-cancerous state and pre-cancerous lesions. The precancerous state of stomach includes 1, chronic atrophic gastritis, 2, pernicious anemia, 3, gastric polyps: although adenomatous or villous polyps account for a small proportion of gastric polyps, the cancer rate is 15% to 40%. The cancer rate is higher for those with a diameter greater than 2cm. Hyperplastic polyps are common, while the cancer rate is only 1%. 4.Residual gastric: The cancer that occurs in the residual stomach after surgery for benign gastric lesions is called residual gastric cancer. The incidence rate increases significantly after gastric surgery, especially from 10 years after surgery. 5.Benign 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.Menetrier’s disease of giant gastric mucosal fold: serum protein is lost through giant gastric mucosal fold, and there is hypoproteinemia and swelling clinically, and about 10% can be cancerous. Pre-cancerous lesions of the stomach include 1. anaplasia and interstitial lesions: the former is also called atypical hyperplasia, which is a reversible pathological cell proliferation caused by chronic inflammation, and a few cases are not carcinogenic. Gastric interstitial anaplasia has more chances of carcinogenesis. 2.Intestinal metaplasia: there are two types: small intestine type and large intestine type, small intestine type complete type, with the characteristics of small intestine mucosa, and better differentiation. Incomplete type of large intestine is similar to large intestine mucosa and can be divided into two subtypes: type IIa, which can secrete non-sulfated mucin; type IIb, which can secrete sulfated mucin, and this type is closely related to the occurrence of gastric cancer. Some people may ask, is gastric cancer contagious? Generally speaking, stomach cancer is not contagious. There is a saying that gastric cancer is contagious, but there is no sufficient evidence to prove this claim.