Smoking (20%): In 1922, Hampeln found that continuous smoking and inhalation of dust can stimulate the bronchial epithelium to induce cancer, and in 1924, Moller used tar to coat the back of rabbits and found a slight increase in the incidence of their lung cancer, and it is now believed that smoking is the most basic high-risk factor for lung cancer, there are more than 3000 chemicals in tobacco, and multi-chain aromatic hydrocarbons (e.g., benzopyrene ) have strong carcinogenic activity and can act on certain specific enzymes within human tissues (especially lung tissues) to produce mutations in cellular molecular structures (e.g., DNA), possibly with mutations in K-ras. Occupational and environmental exposure (10%): It is estimated that up to 15% of lung cancer patients have a history of environmental and occupational exposure, and there is sufficient evidence to confirm that the following nine industrial components increase the incidence of lung cancer: by-products of aluminum products, arsenic, asbestos, bis-chloromethylether, chromium compounds, coke ovens, mustard gas, nickel-containing impurities, vinyl chloride, chronic exposure to beryllium, cadmium, silicon Formalin and other substances can also increase the incidence of lung cancer. In addition, air pollution, especially industrial exhaust is a high risk factor for lung cancer. Radiation (20%): Uranium and fluorite miners exposed to inert gas radon gas, decaying uranium by-products, etc. have significantly higher incidence of lung cancer than others, but people exposed to ionizing radiation do not increase the incidence of lung cancer. Chronic lung infections (15%): Patients with tuberculosis, bronchiectasis, etc., the bronchial epithelium may metamorphose into squamous epithelium during chronic infection and eventually cause cancer, but such cases are rare. Intrinsic factors (5%): Family, genetic and congenital factors as well as reduced immune function, metabolic and endocrine dysfunction may also be high risk factors for lung cancer. Atmospheric pollution (10%): The incidence of lung cancer is high in industrially developed countries, higher in cities than in rural areas, and higher in factories and mines than in residential areas, mainly due to the pollution of the atmosphere by harmful substances such as benzo(a)pyrene carcinogenic hydrocarbons produced by the combustion of oil, coal and internal combustion engines and asphalt road dust in industrial and traffic developed areas. Atmospheric pollution and paper cigarette smoking may contribute to each other and play a synergistic role in the incidence of lung cancer.