{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Carcinoembryonic antigen is a glycoprotein involved in cell adhesion. It is normally produced during fetal development in the gut, but the production of CEA stops before birth. Therefore, it is not usually present in the blood of healthy adults, although levels are raised in heavy smokers. CEA is re-expressed in increased amounts in intestinal carcinomas and several other tumors."}]}]}