At present, most of the tumor markers used in clinical application only have reference value for the diagnosis of some tumors, i.e. auxiliary diagnostic significance. Patients with abnormally elevated tumor markers need further examination to confirm the diagnosis, while for patients with most malignant tumors such as lung cancer, specific and sensitive tumor markers have not been found so far. In other words, spending a lot of money to test several tumor markers does not really exclude malignant tumors if the results are negative. Therefore, it is currently recommended that certain tumor markers be selectively tested in high-risk groups with a high risk of lung cancer. People at high risk for lung cancer (especially men over 40 years of age who are long-term or heavy smokers) include: 1. irritating cough for 2-3 weeks for which anti-inflammatory and cough suppressant treatments are ineffective; 2. pre-existing chronic respiratory disease with a recent change in the nature of the cough; 3. persistent blood in the sputum for the last 2-3 weeks with no other explanation; 4. pneumonia at the same site with recurrent episodes; 5. lung abscess of unknown origin without toxic symptoms, without massive 5. lung abscess of unknown origin, without toxic symptoms, without a large amount of pus sputum, without a history of foreign body inhalation, and with poor efficacy of anti-inflammatory treatment; 6. joint pain in the extremities and pestle-like fingers (toes) of unknown origin; 7. limited emphysema or pulmonary atelectasis on X-ray; 8. isolated round lesions in the lungs and unilateral increased hilar shadow; 9. pleural effusion without toxic symptoms, bloody and progressive increase; 10. stable original tuberculosis lesions and new large lesions in other parts of the lungs.