CEACAM5 and lung cancer: For example, carcinoembryonic antigen (CEA) is one of the most important tumor biomarkers related to colon cancer, lung cancer and ovarian cancer (Tan et al., 2009; Grunnet and Sorensen, 2012; Sorensen et al., 2016) CEA is usually produced in gastrointestinal tissues during fetal development, but it stops after birth.