Lung cancer has become one of the leading causes of cancer deaths in humans, and in China, lung cancer is the number one cancer, accounting for more than 20% of cancer deaths, with more deaths from lung cancer each year than from breast, prostate and bowel cancers combined. In recent years, the incidence of lung cancer is on the rise worldwide. According to the latest statistics, the growth of lung cancer among all types of tumors in China was the most significant in 2005, with an increase of 27% for men and 38% for women. Lung cancer has become the number one cancer killer worldwide. The prognosis of lung cancer is closely related to the clinical stage at the time of diagnosis. The 5-year survival rate of early-stage lung cancer patients can reach over 90%, while that of stage I lung cancer patients drops to 60%, while the overall 5-year survival rate of stage II-IV patients decreases from 40% to 5%. Therefore, “early detection, early diagnosis and early treatment” is an important measure to reduce the mortality rate of lung cancer. Can lung cancer be prevented? The development of lung cancer is closely related to lifestyle and habits. Currently, tobacco (including cigarettes, cigars or pipes) has been proven to be the main carcinogenic factor in the development of lung cancer, and about 90% of lung cancers are thought to be caused by smoking. A study of smoking in China conducted by the Chinese Academy of Medical Sciences in collaboration with the University of Oxford in the United Kingdom shows that if the current smoking situation in China remains unchanged, nearly 100 million Chinese men aged 0-29 will die from smoking by 2050 in their middle or old age, and millions of women will die, including 15% of those who die from lung cancer. In general, when smokers quit smoking, their risk of developing lung cancer decreases. In addition to smoking, environmental factors such as exposure to environmental tobacco smoke (passive smoking), and exposure to asbestos or radon (a radioactive gas that occurs naturally in soil and rocks) can also increase the risk of lung cancer. In addition, many bad habits, such as alcohol abuse, excessive consumption of fatty foods, gross fiber and vitamin intake, irregular life, and excessive psychological stress, are closely related to the development of cancer. Are there any symptoms in the early stage of lung cancer? Cough, hemoptysis, chest pain and discomfort are its common symptoms, but they are often ignored by patients. Cough, which is the earliest and most common symptom of lung cancer patients, is not easy to attract attention because it often resembles cold or bronchitis when it starts. Hemoptysis is the second common symptom of lung cancer, which is often caused by the invasion of cancer tissue into the bronchial mucosa, often as blood sputum, and can last for weeks or months or have intermittent episodes. Due to the small amount or intermittent occurrence of hemoptysis, it is easy to be neglected. In fact, about half of those who present with bloody sputum in middle age or older are due to lung cancer. Therefore, it is important not to be paralyzed when unexplained sputum and blood appear. Chest pain accounts for more than half of lung cancer patients, especially in peripheral lung cancer, chest pain can be the first symptom. Therefore, if there is chest pain in a fixed area for unknown reasons, corresponding examination should be conducted as early as possible. What kind of people should have regular checkups? All people over 40 years old, regardless of gender, smoking or not, and whether they have symptoms or not, should participate in annual health checkups as long as they are financially permissible, and one of the important items is chest X-ray. Those who smoke, have family history and feel unwell, especially those who are older than 60 years old, should have regular checkups so that doctors can make early diagnosis of lung cancer and other lung diseases. Is there any method for early diagnosis of lung cancer? In recent years, early diagnosis of lung cancer has become possible due to theoretical and technological advances in the fields of biology and imaging. The limit of detection of nodules in the lung by chest X-ray is greater than 1 cm in diameter, when the tumor may have invaded the bronchial epithelium and vascular epithelium. Compared to plain chest radiography, chest CT is more effective in detecting peripheral lung lesions. The literature reports that low-dose CT is 10 times more sensitive than plain chest radiographs in detecting small nodules in the lung. Currently, this technology has been applied to lung cancer screening studies in Japan and the United States. It has been demonstrated that low-dose CT can detect more lung cancers and more resectable early lung cancers by CT screening than the previous application of chest X-ray plus sputum cytology. Therefore, it has been recommended that smokers older than 60 years of age should undergo annual low-dose spiral CT screening. Percutaneous fine-needle aspiration biopsy is extremely accurate in diagnosing malignant nodules in the lung, with a sensitivity of 70% to 100%, but is invasive and has certain complications, such as pneumothorax and hemoptysis. Sputum cytology is the use of sputum examination to look for cancer cells, especially multiple sputum examinations, and is helpful in diagnosing central tumors originating in the large airways, such as squamous carcinoma and small cell carcinoma. Peripheral tumors originating from small airways, such as adenocarcinoma, are especially of diameter.