Carcinoembryonic antigen (CEA) is a glycoprotein involved in cell adhesion. It is normally produced during fetal development, 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. Carcinoembryonic antigen (CEA) is one of the most frequently used serum tumor markers for carcinoma, particularly in colorectal cancer. It is useful in the diagnosis and monitoring of cancer, however, specificity for CEA assays is not absolute. Therefore, it is often used in conjunction with tests for other markers.
Since cancer prevalence in a healthy population is low, an elevated CEA has an unacceptably low positive predictive value, with excess false positives. Also, since elevated CEA occurs in the advanced stage of incurable cancer but is low in the early, curable disease, the likelihood of a positive result affecting a patient's survival is diminished. CEA has been suggested in having prognostic value for patients with colon cancer.
Although not satisfactory for screening a healthy population, CEA has been used to monitor recurrence. Determinations of CEA should be done frequently at a minimum of every 3 months. Elevations above baseline should be verified rapidly to exclude laboratory error.
The CEA is of some use as a monitor in treatment. Usually the CEA returns to normal within 1 to 2 months of surgery, but if elevated levels are persistant, disease may be indicated. The test is not infallible in patients treated with radiotherapy and chemotherapy but can be useful in those whose tumor is not measurable.