Lung cancer is a common malignant tumor of the lung. Most lung cancers originate from the bronchial mucosa epithelium, so it is also called bronchial lung cancer. However, there are also a few cancers originating from alveolar epithelium or bronchial glands. Due to the influence of various unfavorable factors, it can cause the overgrowth of normal tracheal mucosal epithelium, followed by abnormal proliferation, and these two lesions are called precancerous lesions. If the adverse factors are lifted, the precancerous lesions can gradually reverse and become normal cells; on the contrary, if the stimulating factors persist, they can be transformed into early carcinoma (carcinoma in situ, i.e. carcinoma not exceeding the submucosa) and continue to develop into invasive carcinoma. Since early stage patients have no symptoms, generally more than 80% of them are at advanced stage when found. Figure: Evolution of lung cancer In the process of growth, the cancer extends along the bronchial wall and invades the adjacent lung tissues through the bronchial wall to form a mass, and at the same time bursts into the bronchus to cause luminal 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 the lymphatic and blood channels or spread to other lung lobes through the whistle. The growth rate and metastatic spread pathways of cancer depend on the histological type, differentiation degree and other biological characteristics of the cancer. The distribution of lung cancer: right lung is more than left lung, and lower lobe is more than upper lobe. Lung cancer originating from the main bronchus and lobe bronchus is called central type lung cancer. Lung cancer originating from the distal side of the bronchus of the lung segment and located in the peripheral part of the lung is called peripheral type lung cancer.