CEACAM5 and lung cancer: Up to now, there are some non-specific tumor biomarkers such as carcinoembryonic antigen (CEA), neuron-specific enolase (NSE), cytokeratin 19 fragments (CYFRA 21-1), progastrin-releasing peptide (proGRP) and so on, which may promote the early diagnostic rate of lung cancer, but it remains elusive to find the specific markers for the diagnosis of lung cancer (Diamandis et al., 2008).