Causes of lung cancer 1. Smoking 85-90% of lung cancers are related to smoking. Therefore, long-term smoking or second-hand smoke can lead to the proliferation of bronchial mucous membrane epithelial cells and induce squamous epithelial carcinoma or undifferentiated small cell carcinoma. 2.Chronic lung diseases Research shows that the incidence of lung cancer in patients with tuberculosis, silicosis and pneumoconiosis is higher than that of normal people, which may be due to chronic inflammation of lung bronchus and lung fiber scar lesions that may cause squamous epithelial metaplasia or hyperplasia during the healing process, on the basis of which some cases may develop into tumors. 3.Intrinsic factors Genetic, immune and endocrine reasons can also be the causative factors for lung cancer. 4.Occupational factors Long-term exposure to radioactive substances such as uranium, radium and their derivatives, carcinogenic hydrocarbons arsenic, chromium, nickel, copper, tin, iron, coal tar, asphalt, petroleum, asbestos, mustard gas and other substances can induce lung cancer. To prevent the occurrence of lung cancer: 1. stay away from tobacco, so that quitting smoking starts from me and around me; 2. pay attention to physical examination, early detection and early treatment of chronic lung diseases; 3. those who have family history of lung cancer should have regular physical examination, and strive for early diagnosis and treatment. In daily life, we should maintain healthy and regular living habits and good mood, and avoid immune deficiency and endocrine diseases caused by bad living habits and depressive state; 4. Do a good job in occupational protection, and take effective protective measures for workers in mines where radioactive ores are mined and exposed to carcinogenic compounds.