CEACAM5 and cancer: Serum biomarkers provide valuable information about the diagnosis and prognosis of a wide variety of malignant tumors, and the best known and most widely studied tumor markers of lung cancer are carcinoembryonic antigen (CEA), SCC antigen, cytokeratin-19 fragments (Cyfra21-1) and neuron-specific enolase (NSE) [5,6].