The stomach is a digestive organ located in the upper left side of the abdomen and is a sac-like cavity that is connected to the lower part of the esophagus by the diaphragm, which is called the cardia. The stomach is divided into 5 parts: the cardia, fundus, body, sinus and pylorus (the exit of the stomach) in that order. The glandular cells in the first three parts secrete gastric acid and digestive enzymes, which constitute gastric juice and help digest and absorb food. The stomach is shaped like a crescent and has two curves, upper and lower. The upper curve is called the lesser curve of the stomach and the lower curve is called the greater curve of the stomach. Tumors can occur in any part of the stomach, but patients with tumors in different parts of the stomach show different symptoms and have different treatment methods and effects. Stomach is adjacent to colon, liver, spleen and pancreas, therefore, stomach cancer often affects these organs. Gastric cancer is the cancer of the epithelial cells of stomach. It is the most common gastrointestinal tumor in China, with the majority of male patients, and the ratio of male to female is (2~3):1. The peak age of incidence is 40~60 years old. The disease is higher in the north than in the south, and higher in the coast than in the interior of China, with the highest incidence in Gansu, Qinghai and Ningxia in the northwest, followed by the northeast, Inner Mongolia and north China. Risk factors 1. Chemical factors mainly include polycyclic aromatic hydrocarbon compounds and nitroso compounds, which are chemical carcinogens that can contaminate food or form during food processing. For example, smoked foods, fried, pickled and moldy foods contain high levels of polycyclic aromatic compounds and nitroso compounds, mainly 3 and 4 benzo(a)pyrene and aflatoxin, which can cause precancerous lesions such as intestinal epithelial hyperplasia of gastric mucosa and heterogeneous hyperplasia of gastric mucosa. 2.Dietary factors Stomach is an important digestive organ, and the food taken in by mouth stays in the stomach for the longest time and has the most chances to contact with gastric mucosa. Therefore, the relationship between the type of food structure and stomach cancer is also greater. (1) Unbalanced diet: high salt diet and pickled foods such as salted fish, pickled vegetables, cured meat and excessive intake of animal fat, overeating and other factors damage the gastric mucosal barrier causing gastric mucosal edema. (2) habitual consumption of fried food, smoked food, moldy grain and oil products. (3) Food is too hot, too hot, eating too fast and habitual consumption of raw, cold, hard, spicy, irritating and rough food can directly damage the gastric mucosa. (4) Lack of fresh vegetables and fruits in the diet, resulting in vitamin deficiency, is a risk factor for the occurrence of gastric cancer. For example, vitamin C and E can inhibit the formation of nitrosamines, which are carcinogenic substances in the stomach. (5) Research data from Mexican scholars show that eating large amounts of chili peppers is closely related to the development of gastric cancer, and capsaicin in chili peppers may be the main substance that induces gastric cancer. (6) The increase of trace elements such as nickel, zinc and cobalt in the diet is also positively correlated with the incidence of gastric cancer. 3. Helicobacter pylori can produce a variety of cytotoxic and immune factors, which is a risk factor for gastric cancer. It was found that the detection rate of Helicobacter pylori in patients with severe chronic atrophic gastritis was as high as 63%. 4. Genetic factors show aggregation of gastric cancer in a few families. That is, those with family history of gastric cancer. Smoking is a risk factor for gastric cancer, and its relative risk is from 1.4 to 4.8, and tends to increase with the increase of smoking volume. 6.Drinking alcohol can promote the dissolution and absorption of carcinogens. At the same time, drinking large amounts of alcohol can damage the gastric mucosa and cause gastritis and gastric ulcers. Alcohol can also inhibit the immune function of the body, leading to the decrease of the immune monitoring function of the body against tumors. Abnormal manifestations 1. Upper abdominal pain is the most common symptom of gastric cancer. About 80% of early gastric cancer patients have this symptom. Initially, it only feels discomfort in the upper abdomen, or a sense of swelling and heaviness, and sometimes there is a vague pain in the heart fossa. Ease of satiety means that although patients feel hungry, they feel full and uncomfortable when they eat a little, which is a manifestation of the involvement of the stomach wall. 2.Loss of appetite and weakness This is a common non-specific symptom of gastric cancer, sometimes it can be the first symptom, accounting for 40% of early gastric cancer. Patients often restrict their diet automatically due to fullness and belching after eating, and lose weight, and sometimes may become anorexic with the progress of the disease. 3.Difficulty in swallowing and progressive worsening of dysphagia and food reflux are the manifestations of lesions located in the culpable portal and involving the lower part of esophagus. 4.Nausea and vomiting in the early stage are only stomach fullness and mild nausea, but when sinus cancer causes pyloric obstruction, it may vomit rotten and foul-smelling overnight food. 5.Vomiting blood and black stool are mostly due to chronic and small bleeding of capillaries and continuous positive fecal occult blood. When tumor invades large blood vessels, large amount of vomiting blood and black stool will appear, and the incidence of hemorrhage is 7%~9%. This symptom accounts for about 20% of early gastric cancer. 6. Diarrhea occurs in about 10% of patients because of low gastric acid or lack of gastric acid, which is mostly thin stool, 2~4 times a day. 7.Distension and fullness of lower abdomen are the manifestations of ascites caused by metastasis of cancer to liver and peritoneum. 8.Systemic symptoms such as emaciation, weakness, anemia, fever, cachexia, etc.