The causative factors of gastric cancer have been found to be broadly related to the following: 1. Helicobacter pylori (HP) infection: Countries and regions with high HP infection rate often have higher incidence of gastric cancer, and the risk of gastric cancer increases accordingly with the increase of HP antibody titer. However, the mechanism of how HP induces the occurrence of gastric cancer is not fully understood. Chemical factors: Nitrosamines and polycyclic aromatic hydrocarbons can cause cancer. 3.Dietary factors: they are the main causes of gastric cancer, among which nitroso compounds are the most common ones. 4.Geographical and genetic factors: the incidence rate is high in three East Asian countries, while it is relatively low in Europe and America. 5.Stomach precancerous lesions and precancerous diseases: precancerous lesions refer to the pathological histological changes of gastric mucosa that are prone to cancer, which are recognized as high-grade intraepithelial neoplasia. Precancerous diseases refer to clinical conditions with significantly increased risk of gastric cancer, such as gastric ulcer, gastric polyp, atrophic gastritis, residual stomach, etc.