Colon cancer is a common malignant tumor of the gastrointestinal tract that occurs in the colon, accounting for the third most common gastrointestinal tumor. It is most common in the rectum and the junction of rectum and sigmoid colon, accounting for 65% of cases after the age of 40, and the ratio of men to women is 2~3:1. The incidence rate is highest in the age group of 40~50. According to the world epidemiological survey, colon cancer has the highest incidence rate in North America, Western Europe, Australia and New Zealand, ranking the first two in visceral tumors, but the incidence rate in Asia, Africa and Latin America is very low. The incidence and mortality rate in China are lower than those of stomach cancer, esophageal cancer, lung cancer and other common malignant tumors. Information from various places shows that with the improvement of people’s living standard and the change of diet structure, its incidence rate is on the trend of each year. (I) General morphological classification According to the general morphology, colon cancer can be divided into three types: mass type, infiltrative type and ulcerative type: 1. Mass type: the tumor grows into the intestinal cavity, is hemispherical or spherical in shape, and has a soft texture. And the tumor is large, easy to ulcerate and bleed and secondary infection and necrosis. This type of colon cancer is usually found in the right hemicolectomy, most of them are highly differentiated, less infiltrative and grow more slowly. 2.Infiltrative type: the tumor invades around the intestinal wall and grows along the submucosa, with a hard texture, easily causing intestinal stenosis and obstruction. The cells of this type of colon cancer are less differentiated, more malignant, and metastasis occurs earlier. It mostly occurs in the large intestine other than the right half colon. 3.Ulcerous type: It is the most common type of colon cancer, which is usually found in the left half colon and rectum. The tumor grows deep into the intestinal wall and infiltrates outside the intestinal wall, and ulcers can appear at an early stage, with elevated edges and deep bottom, easily bleeding and infected, and easily penetrating the intestinal wall. The cells of this type have low differentiation and metastasis occurs earlier. (B) Histological typing According to the histological characteristics, colon cancer can be divided into three types: adenocarcinoma, mucinous carcinoma and undifferentiated carcinoma: 1. Adenocarcinoma: Most of the colon cancers are adenocarcinoma, and the adenocarcinoma cells are arranged into glandular tubular or glandular follicular shape. According to the degree of differentiation, it is classified into grade I~IV according to Broder method, i.e. low malignancy (highly differentiated), moderate malignancy (moderately differentiated), high malignancy (poorly differentiated) and undifferentiated cancer. 2.Mucinous carcinoma: Cancer cells secrete more mucus, which can be in the extracellular mesenchyme or collected in the cell to squeeze the nucleus toward the edge, and those with more intracellular mucus have poor prognosis. 3.Undifferentiated carcinoma: The cells of undifferentiated carcinoma are small, round or irregular in shape, and arranged into untidy sheets. They have low differentiation, strong infiltration and can easily invade small blood vessels and lymphatic vessels, so the prognosis is very poor.