Tumor markers are antigens and bioactive substances produced by tumor tissues and cells due to abnormal expression of oncogenes, oncogenes or other tumor-related genes and their products. They mainly include tumor antigens, proteases, hormones, receptors, cytokines and so on. They are bioactive substances produced by tumor tissues or reflect the presence of tumor itself. The activity or content of these substances can be detected in the tissues, body fluids and excreta of patients. Many tumor cells have a characteristic that they can continuously produce and secrete some special substances released into the blood. The presence or absence and amount of these substances sometimes correlate with the presence or absence and extent of the disease. But unfortunately, so far, there is no single substance directly related to the development or condition of lung cancer. Therefore, it is important not to worry too much about whether you are suffering from neoplastic disease because of a single increase of one tumor marker. Commonly used serum tumor markers for lung cancer screening and detection include: CA199, CA242, CEA, NSE, CYFRA211, TPA and so on. These markers are not directly related to lung cancer and can only be used as a screening indicator to indicate the possible presence of tumors. An ideal tumor marker should have the following conditions: 1. good tumor specificity, preferably also with tissue specificity. 2.Ability to monitor almost all tumor cells, especially early cancerous cells, so that it can be used for early tumor screening. 3.The level of expression, synthesis and release of the substance should be correlated with the tumor load. 4.The monitoring method of the substance should be highly specific and sensitive, simple and fast to operate. So far, no tumor marker has been found to meet the above criteria at the same time. Therefore, in clinical practice, multiple tumor markers are usually used in combination to improve the accuracy of diagnosis.