CEACAM5 and lung cancer: The detection of tumor markers, such as carcinoembryonic antigen (CEA), cytokeratin fragment antigen 21-1 (CYFRA21-1), squamous cell carcinoma antigen (SCC), progastrin-releasing peptide (Pro-GRP), carbohydrate antigen 125 (CA125), and neuron-specific enolase (NSE), for lung cancer is widely used in clinical practice (14–17); however, it can easily cause errors in clinical diagnosis owing to its relatively low specificity.