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carcinoembryonic antigen A protein found in many types of cells that is associated with a developing fetus and tumors and measurable by blood testing. Abbreviated CEA. Conditions that increase CEA include smoking, infection, inflammatory bowel disease, pancreatitis, cirrhosis of the liver, and some benign tumors (in the same organs that have cancers with increased CEA). The normal level is less than 2.5 ng/ml (nanograms per milliliter) in an adult nonsmoker and less than 5.0 ng/ml in a smoker. Benign disease rarely elevates the CEA over 10 ng/ml. The main use of CEA test is as a tumor marker, especially with intestinal cancer. The most common cancers that elevate CEA are in the colon and rectum. Others include cancer of the pancreas, stomach, breast, and lung, as well as certain types of thyroid and ovarian cancer. Levels over 20 ng/ml before therapy are associated with cancer that has already metastasized (spread). CEA tests are useful in monitoring the treatment of CEA-rich tumors.