CLINICAL SIGNIFICANCE:
Carcinoembryonic antigen (CEA) is a protein found in many types of cells but associated with tumors and the developing fetus . CEA is a protein that normally occurs in fetal gut tissue. After birth, detectable serum levels essentially disappear. However, CEA may increase in the presence of various disorders such as colon cancer. This test may also be used to determine the responsiveness of cancer patients to treatment (to determine if cancer is spreading or going into remission). The CEA was one of the first oncofetal antigens to be described and exploited clinically. It is a complex glycoprotein of molecular weight 20,000, that is associated with the plasma membrane of tumor cells, from which it may be released into the blood .
Although CEA was first identified in colon cancer, and abnormal CEA blood level is specific neither for colon cancer nor for malignancy in general. Elevated CEA levels are found in a variety of cancers other than colonic, including pancreatic, gastric, lung, and breast. It is also detected in benign conditions including cirrhosis, inflamatory bowel disease, chronic lung disease, and pancreatitis. The CEA was found to be elevated in up to 90 per cent of smokers and in 3 per cent of a healthy control population. Thus, the test for CEA cannot substitute for a pathological diagnosis.
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. The CEA has been sugested as having prognostic value for patients with colon cancer. Preoperative CEA values have been positively correlated with stage and negatively correlated with disease free survival.
Although not satisfactory for screening a healthy population, CEA has been used to monitor recurrence. Early data suggested that CEA predicted clinical relapse by several months. Subsequently, several investigators have examined intensive, serial CEA monitoring as an indicator for second look surgery in the hope that relapse could be detected at a time when surgical resection for cure was still possible. Criteria for reoperation included a significant rise of CEA above a base line level on serial determinations and absence of obvious unrespectable disease on staging workup. Determinations of CEA should be done frequently: at a minimum of every 3 months and if possible every 1month to 2 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 it returns elevated persistent 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. The CEA is often positve in malignancies other than colonic. In cancer of the breast, lung, pancreas, stomach and ovary the CEA may be elevated and can be used to monitor the progress of disease or response to treatment.
What abnormal result mean:
- Colon cancer
- Breast cancer
- Lung cancer
- Pancreatic cancer
- Thyroid cancer
- Genitourinary carcinomas
- Inflammatory gastrointestinal diseases (for example, ulcerative colitis, diverticulitis, cholecystitis, pancreatitis)
- Cirrhosis
- Other liver disease
- Peptic ulcer
- Heavy smoking
- Pulmonary infections
A single abnormal CEA value may be significant, but must be regarded cautiously. In general, very high CEA levels indicate more serious cancer, with a poorer chance for cure. But some benign diseases and certain cancer treatments may produce an elevated CEA test. Cigarette smoking will also cause the CEA level to be abnormally high.