High-risk group of lung cancer: Men over 40 years old who are long-term heavy smokers (smoking index > 400 cigarettes per year), the smoking index is the number of cigarettes smoked per day multiplied by the number of years of smoking, and those who have the following conditions should be treated as suspected lung cancer subjects for relevant cancer screening: 1. irritating cough without obvious causes lasting 2 to 3 weeks, and treatment is ineffective. 2.Or chronic respiratory disease with a change in the nature of the cough, such as a change in tone. 3.Persistent or recurrent sputum and blood in a short period of time without other causes to explain. 4.Recurrent episodes of pneumonia at the same site, especially segmental pneumonia. 5.Pulmonary abscess of unknown cause, without toxic symptoms, without large amount of pus sputum, without history of foreign body inhalation, and without significant effect of anti-inflammatory treatment. 6.Unexplained joint pain in the extremities and pestle-like fingers (toes). 7.Limited emphysema or segmental or lobar pulmonary atelectasis on X ray. 8, isolated round lesions and unilateral increased hilar shadow. 9, original pulmonary tuberculosis, lesions have been stabilized, and the morphology or nature has changed. 10, no toxic symptoms of pleural effusion, especially bloody, progressive increase.