Colorectal cancer is a malignant tumor that seriously threatens human life and health, and ranks the 3rd in incidence rate among all kinds of malignant tumors. In recent years, with the development of economy and the improvement of people’s living standard, the incidence rate of colorectal cancer has shown a trend of increasing year by year. (a) Risk factors of colorectal cancer: including genetic and environmental aspects. 1, familial adenomatous polyposis (FAP) and hereditary non-polyposis colorectal cancer (HNPCC): less than 1% of colorectal cancers are related to FAP, while HNPCC accounts for 2%-6% of colorectal cancers. According to statistics, 90% of patients with untreated FAP have developed colon cancer by the age of 45, while HNPCC also features a low age of onset, with a median age of 48 years, and some patients develop the disease at the age of 20. Zhou Jianfeng, Department of Medical Oncology, Peking Union Medical College Hospital 2. Personal or family history of sporadic colorectal cancer and adenomatous polyps: 1.5%~3.0% of colorectal cancer patients develop a second primary colorectal cancer within 5 years after surgery. The incidence of colorectal cancer was also significantly higher in patients with a history of adenomatous polyps or villous/mixed adenomas of 1 cm or greater in diameter than in the general population. Another study showed that the risk of colorectal cancer is 1.7 times higher in the general population when there is a patient with colorectal cancer in the immediate family, and the risk is further increased when the age of onset of the disease in the immediate family is less than 55 years old or when there are two patients with the disease, and a family history of colorectal adenomatosis also has the significance of increasing the risk of colorectal cancer. 3. Inflammatory bowel disease: the incidence of colon cancer increases with the prolongation of the disease and the expansion of the lesions in ulcerative colitis. The risk of colon cancer in total colitis is 5-15 times higher than that in the general population, while the risk in patients with left hemicolectomy is 3 times higher; it is estimated that the incidence of colon cancer in patients with ulcerative colitis of 10-20 years’ duration is 0.5%, and increases to 1% thereafter. Diabetes and insulin resistance: The results of a meta-analysis showed that the incidence of colorectal cancer was 30% higher among 2,593,935 participants with diabetes than with non-diabetes, and the possible mechanism is that insulin is an important growth factor for colonic mucosal cells and has a stimulating effect on colonic tumor cells. Alcohol consumption: A pooled analysis including eight independent studies showed that alcohol consumption moderately increases the risk of colorectal cancer, especially when the daily alcohol intake exceeds 45 grams. Alcohol consumption may increase the risk of colorectal cancer and alcohol may interfere with the intake and absorption of folic acid. 6, obesity: the results of at least two large prospective studies show that the risk of colon cancer increases 1.5 times in obese compared to normal weight people. 7.Other: such as smoking, high intake of red meat and fat, pelvic radiotherapy, ileal substitution bladder, etc. (2) Prevention of colorectal cancer: By reducing and eliminating the pathogenic factors of colorectal cancer and inhibiting the cancer process of normal cells. 1. Dietary adjustment ① Reduce energy intake: energy intake is related to the occurrence of colorectal cancer. Most studies have shown that total energy intake is related to the risk of colorectal cancer, regardless of whether the energy intake is protein, fat or carbohydrate. Reducing energy intake has the potential to reduce the incidence of colorectal cancer. ②Reducing fat and red meat intake: The occurrence of colorectal cancer is closely related to animal fat and meat, and some studies have shown that the risk of colorectal cancer is 3.26 times higher in those with high fat intake than those with low fat. And the intake of red meat is a strong risk factor for the occurrence of colorectal cancer. Reducing the fat content in food, especially minimizing brown meat after frying and roasting, can help reduce the chance of colorectal cancer. ③Increase fruits, vegetables and dietary fiber: fiber can increase the amount of stool, dilute carcinogens in the colon and adsorb bile salts, thus can reduce the occurrence of colorectal cancer. Epidemiological data show that the risk of colorectal cancer in those with the highest fruit and vegetable intake is only half of that in those with the lowest. Therefore, in the usual diet, we should try to consume more vegetables, fruits and fiber and have a reasonable diet to reduce the occurrence of colorectal cancer. ④Vitamins and trace elements: Some studies have shown that supplementation with vitamins A, C and E can transform the excessive proliferation of colonic epithelium in adenoma patients into normal, but the current information does not support the use of antioxidant vitamins to prevent colorectal cancer. Folic acid reduces the incidence of colorectal cancer, but the exact mechanism is not known. Another study found that increased intake of calcium and magnesium may reduce the incidence of colorectal cancer, but the study is not well-detailed. ⑤ Dietary anti-carcinogens: dietary garlic, onions, leeks and shallots contain thioether; citrus contains terpenes; grapes, strawberries, apples contain plant phenols as well as carrots, diosgenes, and watermelon contains carotenoids, all of which are believed to be able to inhibit mutations and have anti-cancer effects. Especially garlic, some studies show that garlic is the vegetable with the strongest protective effect to save people from distal colon cancer. 2.Change life habits ① Exercise: Obesity, especially abdominal obesity and low physical activity are the risk factors of colorectal cancer. Weight loss and exercise can play a role in preventing colorectal cancer. ② Quit drinking and smoking 3.Drugs Many epidemiological studies have shown that the incidence of colorectal cancer is reduced in long-term users of non-steroidal anti-inflammatory drugs. However, the dosage, duration of administration and side effects caused by long-term application of NSAIDs need to be further studied. 4.Treatment of precancerous lesions Patients with ulcerative colitis, personal or family history of colorectal cancer or adenoma have an increased risk of colorectal cancer, and through screening and follow-up, early removal of adenoma and treatment of colitis can reduce the incidence and mortality of colorectal cancer. Especially for those with family history, screening high-risk groups through genetic examination and performing colonoscopy are important aspects of colorectal cancer prevention.