The occurrence of tumor is closely related to the environment in which patients live. The theory of environmental carcinogenesis believes that about 80%-90% of human malignant tumors are caused by environmental factors, and this theory has been supported by some studies of geo-epidemiology and migration epidemiology. There are many environmental factors related to the occurrence of tumors, which are chemical, physical and biological in nature, among which chemical factors are the major ones. The sources of environmental carcinogens are mainly as follows: 1. Air, water and other environmental pollution water and air are essential elements for human survival, with the development of agriculture and industry, environmental pollution is becoming more and more serious. Many environmental pollutants are carcinogens or carcinogenic substances, such as coal combustion, exhaust gas from motor vehicles and industrial waste gas, which contain carcinogens, mainly polycyclic aromatic hydrocarbons, such as 3,4-benzopyrene. Therefore, many data prove that the mortality rate of lung cancer in industrial cities is higher than that in non-industrial cities and rural areas. 2.Food has a very close relationship with tumor. It is known that mycotoxins, food additives, nitrosamines and toxic components of certain plants in food have carcinogenic and cancer-promoting effects. 3.Occupational exposure In the production environment, there are many kinds of chemical substances, some of which are carcinogenic and can cause occupational cancer due to long-term exposure. However, generally speaking, since the source of occupational cancer is clear, it can be effectively prevented through active preventive measures. 4.Drugs have been found to have pathogenic effects. 5.Bad habits smoking has been proven to increase the incidence of malignant tumors, especially lung cancer. For example, the American Oncology Association reported that the ratio of the mortality rate of malignant tumors between smokers and non-smokers in 45-64 years old is 7.84 for lung cancer, 4.7 for esophageal cancer, and 2.14 for all tumors.