Most cancers are named after the part of the body where they first grow. Lung cancer starts in the lungs and is a common malignancy. The lungs are two spongy organs that grow in the chest cavity and are the body’s breathing airways they bring air in and out of the body, taking in oxygen and eliminating the useless product, carbon dioxide. The right lung has three parts, called lobes. The left lung has two lobes. The left lung is smaller, and that is because the heart takes up more space on the left side of the body. The lining that surrounds the lungs is called the pleura and helps protect the lungs and allows them to move around inside when you breathe. The trachea carries air down into the lungs. The trachea divides into tubes called bronchi, which then divide into smaller branches called fine bronchi. These small branches end in very small air sacs called alveoli. Most lung cancers originate in the mucosal epithelium of the bronchi, in many cases in the inner layer of the bronchi, but can also occur elsewhere, such as in the trachea, fine bronchi, or alveoli. The lymphatic vessels are closely related to cancer and are more similar to the venous vessels, but they carry lymph rather than blood. Lymph is a clear, bright fluid that contains tissue excretion and immune system cells. The lymphatic vessels of the lungs collect in nearby lymph nodes in the chest cavity. These lymph nodes are located around the bronchi and in the mediastinum (the area between the two lungs). Cancer cells can enter the lymphatic vessels and then spread along these ducts to the lymph nodes. The lymph nodes are small, bean-shaped and bring together cells of the immune system, which play an important role in fighting infection. When lung cancer cells reach the lymph nodes, they are able to continue to grow. If cancer cells have multiplied in the lymph nodes, it is likely that the cancer cells have spread to other organs in the body at the same time. In the past 50 years, the incidence and death rate of lung cancer have increased rapidly in the world, especially in industrialized countries, and lung cancer has become the most common cause of death among male patients. 40 years ago, the majority of patients who underwent surgical treatment for lung diseases in China were tuberculosis, followed by bronchiectasis, lung abscess and other purulent infections of the lung, and there were not many cases of lung cancer. In the past 30 years or so, lung cancer has gradually increased among lung resection cases, and has jumped to the first place. According to the statistics of malignant tumors in Shanghai, the incidence of lung cancer has increased sharply among male cancer cases and ranks first. The age of onset of lung cancer is mostly above 40 years old, and men account for most of the cases, and the ratio of men to women is about 5:1. The mortality rate of this disease is high, and the current treatment effect is unsatisfactory. Early detection, early diagnosis and early treatment are important factors to improve the efficacy. The growth distribution of lung cancer is more in the right lung than in the left lung, and more in the lower lobe than in the upper lobe. Lung cancer originating from the main bronchus and lobe bronchus is called central type lung cancer. Lung cancer that originates from the distal part of the bronchus of a lung segment and is located in the peripheral part of the lung is called peripheral lung cancer. Most lung cancers originate from the bronchial mucosa epithelium, but a small number of cancers originate from the alveolar epithelium or bronchial glands. In the process of growth, the cancer extends and expands through the bronchial wall and invades the adjacent lung tissues to form a mass, and at the same time bursts into the bronchial lumen to cause narrowing or obstruction. Further development and spread of the cancer can invade the chest wall, mediastinum, heart, large blood vessels and other adjacent tissues directly from the lung; it can metastasize to other parts of the body through lymphatic and blood channels or spread to other lung lobes through respiratory tract. The growth rate and metastatic spread of cancer depends on the histological type, differentiation degree and other biological characteristics of the cancer. After years of research and study, the following factors are recognized as closely related to the etiology of lung cancer: 1. Smoking According to a large number of research data from various countries, the etiology of lung cancer is closely related to paper smoking. The increase in the incidence of lung cancer has a parallel relationship with the increase in the sale of paper cigarettes. Paper cigarettes contain many carcinogenic substances such as benzo(a)pyrene. The incidence of lung cancer is 10 times higher in smokers than in nonsmokers, and even higher in heavy smokers, 20 times higher than in nonsmokers. At the end of this century, the incidence of lung cancer among female patients in Western European countries has increased significantly with the increasing number of women smokers. Among the clinically diagnosed lung cancer cases, those who smoke more than 20 cigarettes a day for more than 30 years account for more than 80%. The high incidence of lung cancer in industrially developed countries, higher in urban than rural areas, and higher in factories and mines than in residential areas, is mainly due to the pollution of the atmosphere by harmful substances such as benzopyrene carcinogenic hydrocarbons from the combustion of oil, coal and internal combustion engines and asphalt road dust in industrial and transportation developed areas. The survey material shows that the incidence of lung cancer increases in areas with high concentration of benzo(a)pyrene in the atmosphere. 3.Occupational factors After years of investigation and research, it is now recognized that 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 and mustard gas can induce lung cancer, mainly squamous and undifferentiated small cell carcinoma. 4.Chronic lung diseases such as tuberculosis, silicosis, pneumoconiosis, etc. can co-exist with lung cancer. The incidence of cancer in these cases is higher than that of normal people. In addition, chronic inflammation of lung bronchus and lung fiber scar lesions may cause squamous epithelial chemosis or hyperplasia during the healing process, and on this basis, some cases may develop into carcinomas. 5. Intrinsic factors such as family genetics, lowered immune function, metabolic activity and endocrine dysfunction may also play a role in promoting the development of lung cancer.