The causes of lung cancer in situ include smoking, occupational exposure, environmental pollution, family heredity and so on. 1. Smoking: Smoking is the most important cause of lung cancer in situ, and the more the amount of smoking and the longer the time of smoking, the higher the chance of lung cancer. Passive second-hand smoke is also easy to cause lung cancer. 2. Occupational exposure: exposure to arsenic, chromium, asbestos, nickel, microwave radiation and other substances in the working environment may also lead to lung cancer. 3. Environmental pollution: Arsenic oxide, benzo(a)pyrene, sulfur dioxide, nitric oxide and other industrial waste gas and automobile exhaust are also important factors leading to lung cancer. 4. Family heredity: patients with family history of lung cancer have higher chances of suffering from lung cancer than normal people. After suffering from lung cancer in situ, it needs to be treated as early as possible. Long-term delay in treatment may lead to the development of the disease and affect the therapeutic effect.