CEACAM5 and lung cancer: In the Currently, diagnostic methods for lung cancer mainly based on X-ray imaging, percutaneous biopsy, bronchoscope and sputum cytology, etc. Some studies have reported that levels of serum carcinoembryonic antigen (CEA), cytokeratin 19 fragment (CYFRA21-1) and other tumor markers are elevated in some patients with lung cancer, but the sensitivity was about 30%–50% and the specificity is about 60–80% [26], [28]–[29].