CEACAM5 and lung cancer: Serum tumor markers for lung cancer including carcinoembryonic antigen (CEA), cytokeratin 19 fragment (CYFRA 21‐1), carbohydrate antigen 125 (CA 125), squamous cell carcinoma antigen (SCC), neuron specific enolase (NSE), and progastrin releasing peptide (ProGRP) are widely used for diagnosis, but their role as prognostic predictors is still debated.