Malignant tumors have become the number one killer threatening human survival. According to WHO, 1/3 of cancers can be prevented; 1/3 of cancers can be cured if diagnosed early and treated with scientific and comprehensive treatment; 1/3 of cancers can be improved through reasonable and effective palliative treatment. Therefore, prevention is more important than treatment. It is even more important to improve the awareness and self-care ability of people who are prone to tumors and at high risk. Many cancer-causing factors should be controlled or eliminated as much as possible to achieve the purpose of cancer prevention. These requirements are: 1. pay attention to the balance of diet and nutrition and not to be partial; 2. not to eat the exact same diet repeatedly or take the same medicine for a long time; 3. eat moderately and not to be full; 4. not to smoke; 5. consume foods rich in vitamin A, C, E and fiber in appropriate amount; 6. avoid excessive drinking; 7. eat less salty and hot food; 8. eat less burnt food; 9. not to eat moldy food Avoid excessive sun exposure; 11. Avoid overexertion; 12. Maintain personal hygiene and sanitation. What are cancer-risk groups? There are five main groups of people who are prone to cancer: 1. Elderly people have a high incidence of tumors after the age of 50, and the risk of tumors increases with age. 2. People exposed to carcinogenic substances refer to tumors caused by occupational diseases on one hand, such as radiation workers, asbestos workers, printing and dyeing factory workers, etc. On the other hand, they include long-term exposure to benzene and its derivatives. On the other hand, it includes people who are exposed to benzene and its derivatives for a long time, such as people who dye their hair for a long time, people who eat smoked, barbecued and pickled food for a long time, long-term smokers or passive smokers, people who are infected with special viruses, etc. 3. Genetic high-risk groups have higher risk of cancer patients’ offspring than the general population, i.e. people with family history of tumor have higher chance of developing tumor than the general population. Therefore, for people with obvious family history of cancer, they should correct bad habits, reduce or even get rid of the influence of environmental carcinogens, and participate in regular cancer prevention screening. 4.A considerable part of tumor patients suffer from repeated cancer and multiple cancers after treatment, and there may be many precancerous lesions in tumor patients, which keep changing into new lesions. Tumor patients must be regularly reviewed and followed up after treatment in order to detect new lesions or second tumors at an early stage.