Primary bronchial lung cancer, or lung cancer for short, originates in the bronchial mucosa or glands. Lung cancer is a serious threat to human health. According to the information published by the World Health Organization (WHO), lung cancer ranks first in the world in terms of incidence and mortality. From 2000 to 2005, the number of lung cancer cases in China increased by 116,000 and the number of deaths increased by 101,000. At present, lung cancer is still a disease with very poor prognosis, only 15% of patients have limited lesions at the time of diagnosis, and the 5-year survival rate can reach 50%, while more than 85% of patients are found to be in advanced stage and have lost the chance of surgery. 86% of lung cancer patients die within 5 years after diagnosis, and the median survival period of lung cancer patients is 1 to 1.5 years. Therefore, early diagnosis of lung cancer becomes very important. The etiology and pathogenesis of lung cancer are not fully understood, but studies have shown that it is related to the following factors: 1. Smoking: A large number of studies have shown that smoking, especially paper smoking, is the primary cause of progressive increase in lung cancer mortality. Nicotine, benzo(a)pyrene, nitrosamines and a small amount of radioactive elements such as polonium in cigarette smoke have carcinogenic effects, which are especially likely to cause squamous epithelial cell carcinoma and undifferentiated small cell carcinoma. Lung cancer can also be induced by paper cigarette smoke and tar in animal experiments. Compared to nonsmokers, the risk of lung cancer is on average 9-10 times higher in smokers and at least 10-25 times higher in heavy smokers. There is a clear volume-effect relationship between the amount of smoking and lung cancer, with the younger the age of initiation and the higher the amount of smoking, the higher the incidence and mortality of lung cancer. Passive or environmental smoking is also a cause of lung cancer, with a 20-30% increased risk. The risk of lung cancer decreases each year after quitting smoking, and can be halved after 1-5 years of quitting. The incidence of lung cancer decreases progressively during the period from 2-15 years after quitting, and thereafter the incidence is equivalent to that of non-smoking. 2.Atmospheric pollution: In both the United States and the United Kingdom, the lung cancer mortality rate of urban residents is higher than that of rural areas, and it increases with the degree of urbanization. The mortality rate of lung cancer in heavy industrial cities in China is also higher than that in light industrial cities. The association between atmospheric pollution and lung cancer mortality suggests a role of atmospheric pollution in lung cancer development. Carcinogens such as 3,4 benzo(a)pyrene, arsenic oxide, radioactive substances, nickel-chromium compounds, and noncombustible aliphatic hydrocarbons are present in the atmosphere of heavy industrial cities. In heavily polluted big cities, the amount of benzopyrene inhaled by residents in the air daily can exceed the content of 20 paper cigarettes and increase the carcinogenic effect of paper cigarettes. 3.Occupational factors: The special substances related to the development of lung cancer by exposure to industrial production include asbestos, arsenic, chromium, nickel, beryllium, coal tar, mustard gas, trichloromethane, heating products of tobacco, as well as radon and radon gas produced by the decay of radioactive substances such as uranium and radium, ionizing radiation and microwave radiation. These factors can increase the risk of lung cancer by 3 to 30 times. The time from exposure to the occurrence of lung cancer is related to the degree of exposure, usually more than 10 years, with an average of 16-17 years. Among them, asbestos is a world-recognized carcinogen and is probably the most common occupational factor in human lung cancer. The incidence of lung cancer, pleural and peritoneal mesothelioma is higher on average among workers exposed to asbestos, with latency periods of 20 years or more. 4.Diet: Less use of vegetables and fruits containing beta carotene increases the risk of lung cancer. Epidemiological data show that more practical green, yellow and gardenia yellow vegetables and fruits containing beta carotene can reduce the risk of lung cancer, and this protective effect is especially obvious for people who are smoking or former smokers. 5, genetic alterations: lung cancer cells have many genetic damages, including the activation of dominant oncogenes and the inactivation of oncogenes or recessive oncogenes. In fact, lung cancer cells may have multiple genetic abnormalities. Non-small cell lung cancer with ras gene mutation has a poor prognosis, while small cell lung cancer with c-myc gene amplification has a poor prognosis. 6.Other: certain lung diseases are related to the development of lung cancer. Patients with chronic bronchitis have one times higher incidence of lung cancer than those without this disease; adenocarcinoma can occur in tuberculous scar. In addition, viral and fungal infections, reduction of selenium and zinc content in the soil may also be related to the occurrence of lung cancer.