Gastric cancer is the transformation of cells of the stomach into malignant (cancerous) and uncontrolled growth, resulting in the formation of a tumor. Almost all malignant tumors of the stomach (about 95%) originate from the glandular tissue of the stomach. Tumors can travel along, or directly through, the stomach wall and transfer tumor cells into the bloodstream or lymphatic system. Once outside the stomach, the cancer cells will metastasize to other organs. According to the origin of the tissue, the classification of gastric cancer is as follows: 1. The most common is adenocarcinoma – originates from the mucosal glands of the stomach. 2. Lymphoma – originates from lymphocytes (which are blood cells associated with the immune system). 3.Sarcoma – originates from connective tissue (such as muscle, fat or blood vessels). 4.Other types include carcinoid tumor, small cell carcinoma and squamous cell carcinoma. 5.Tumors that metastasize from breast cancer, melanoma and other primary cancers. At present, the exact cause of stomach cancer is not clear, but it is believed that most of them are caused by exposure to carcinogens (especially nitrates). Nitrates are found in many foods (especially sun-dried, smoked, and cured meats). Carcinogens can cause errors in the coding of genes that control growth and repair of cells. A variety of factors increase the risk of gastric cancer, such as: gastritis; pernicious anemia; gastric polyps; chronic gastric ulcers; a family history of gastric cancer; a history of gastrectomy without gastric cancer, such as peptic ulcer; blood type A; precancerous lesions, such as intestinal epithelial hyperplasia; abnormalities in certain genes; and a family history of genetic disorders, such as familial polyposis and hereditary non-polyp colorectal cancer. Gastric lymphoma and gastric adenocarcinoma are associated with H. pylori infection of the gastric mucosa. Infection with H. pylori causes chronic inflammation and ulcers in the stomach. About two-thirds of people in China are infected with this bacterium, and the risk of developing gastric cancer after infection is six times higher than that of non-infected people. Smoking and chronic alcohol consumption also increase the risk of stomach cancer. In addition, workers in the coal, steel and rubber industries are at higher risk of developing stomach cancer. Stomach cancer is common between the ages of 60 and 80 and is more common in China, Japan, Korea, some European countries, and Latin America, while the incidence is lower in the United States and Canada. This may be related to the consumption of cured nitrate-containing foods (especially meat and fish). Stomach cancer detected and treated early will have a longer survival time, but more patients are detected late and the survival time for progressive gastric cancer is not promising.