The five tumor markers for lung cancer include carcinoembryonic antigen, which is more specific for adenocarcinoma, cytokeratin 19, which is more specific for squamous carcinoma, neurospecific enolase, which is more specific for small cell lung cancer, and two other markers for adenocarcinoma, including glycoconjugate antigen 199 and glycoconjugate antigen 125. If the patient has liver metastases, he or she may also have elevated methemoglobin tumor markers. In general, if a patient has thoracic or abdominal metastases that cause a pleural or abdominal effusion, a corresponding increase in glycoprotein 125 will be observed. These tumor markers can play a corresponding role in different stages of the disease and can help to detect tumors in the screening stage of the disease. If tumor markers are elevated again after treatment, it can indicate tumor recurrence and can also be used to monitor the effect of treatment. If the tumor markers gradually decrease after treatment, it indicates that the treatment is effective. If the tumor markers are elevated again after a period of time after treatment, it may indicate that the drug has become resistant or insensitive, suggesting the need to change the treatment regimen.