CEACAM5 and lung cancer: Tumor marker tests, such as carcinoembryonic antigen (CEA), cytokeratin 19 fragment, squamous epithelial cell carcinoma (SCC) antigen, carcinoma antigen 125, neuron-specific enolase (NSE), have been widely used in the diagnosis of lung cancer; however, the sensitivity and specificity of these markers are not high (I & Cho, 2015).