Several serum tumor protein markers have been studied extensively, and are currently available for blood testing, such as carcinoembryonic antigen, serum cytokeratin 19 fragment, and progastrin-releasing peptide, but none of them is satisfactory for diagnosis of early stage lung cancer because of their relatively low sensitivity and specificity in detecting the presence of cancer cells [89-91]. The gene discussed is CEACAM5; the disease is lung cancer.