CEA (carcinoembryonic antigen), CYFRA 21 (cytokeratin fragment), and NSE (neuron-specific enolase) are the most common tumor markers in lung cancer that have greater clinical significance in the assessment of outcome and prognosis. CEA levels are rarely elevated in adult healthy individuals. This makes CEA clinically relevant in the differential diagnosis of non-small cell lung cancer, prognosis assessment, monitoring the efficacy of advanced lung cancer therapy, and early detection of recurrence of lung adenocarcinoma. It is the most sensitive tumor marker for lung cancer, especially for squamous lung cancer, and has significant clinical value for prognosis and efficacy assessment. Studies have shown that elevation of CYFRA 21 precedes the onset of clinical symptoms and imaging findings, such as CT, and can indicate disease progression earlier. NSE is an important marker for the diagnosis of small cell lung cancer, and high levels of NSE (>100 mg/L) indicate the possibility of small cell lung cancer if malignancy is suspected, as well as for the differential diagnosis of ectopic neuroendocrine tumors, hepatocellular carcinoma, lymphoma and seminoma. NSE has a positive diagnostic rate of 66.7% for small cell lung cancer and 80% for extensive stage. Now the question is, what should many people do after finding elevated lung cancer markers during physical examination? Should they have an immediate chest CT examination or a direct PET CT examination? 1.Lung cancer diagnosis still depends on pathological diagnosis, which is the gold standard that cannot be replaced, but tumor markers are already mature technology and have become a routine means as a method of diagnosis, treatment and follow-up. It is worth noting that although there are tumor markers corresponding to lung cancer, they do not rise with a single tumor marker for lung cancer diagnosis and are not unique. The correct method is firstly to dynamically observe the rise of the markers. Tumor markers are substances that already exist in the body and will rise quickly when tumors appear, or several different tumors may cause the rise of the same tumor marker, so the rise of the markers can be dynamically observed. /2. The lung cancer diagnosis and treatment specification has already suggested that when it is not clear whether it is lung cancer, it is recommended to combine multiple tumor markers to find out whether several of them are elevated at the same time, so as to provide more accurate help for clinical diagnosis. If it is found that several lung cancer markers are elevated, then chest CT examination must also be actively performed. 3. Look at the marker levels, for example, a high level of NSE greater than 100 mg/L can highly suspect the possibility of small cell lung cancer; CYFRA 21 is a very good marker with a sensitivity of 100% for non-small cell lung cancer if the level is higher than 3.3 μg/L. If high levels of the above lung cancer markers are found, aggressive CT chest examinations should also be performed. It should be noted that most tumor markers are cross-reactive with each other and are occasionally seen in certain benign diseases and acute and chronic inflammatory conditions. It usually returns to normal in 10-15 days, so there is no need to worry too much.