Carcinoembryonic Antigen (CEA) is a blood protein, which increases in some types of malignancies and may be used as a tumour marker to assess treatment efficacy in colorectal cancer.
Background
Tumour markers are the substances found in the blood that indicate the presence of the tumour and are used to diagnose and monitor malignancies as it changes in blood reflect the growth or shrinking of malignant tissues. One of the most common tumour markers is called carcinoembryonic antigen (CEA). It was described in 1965 by Phil Gold and Samuel O. Freedman. The scientists identified the substance in extracts from the human bowel, particularly part of the large bowel called the colon. As occurred later, CEA is a glycoprotein normally produced during embryonal development and in low concentrations by the colon as well as some other epithelial tissues in an adult. It was noticed that CEA is increased in the blood of patients that have certain tumours such as colorectal (bowel) cancer, breast cancer, prostate malignancies, and lung and thyroid cancers.
CEA test use
The indications for performing the CEA test include the following:
- To assess the stage of cancer, particularly bowel cancer;
- To monitor the results of the cancer treatment and recurrence of the tumour;
- To identify the metastases and dissemination of cancer CEA is measured not only in the serum but in the cerebrospinal fluid, fluids obtained from the chest or belly;
- In combination with other tumour markers may be used to evaluate cancer;
- However, as long as CEA may be elevated not only in cancer but also in many non-cancerous conditions, it cannot be used as the only method to diagnose cancer.
As the levels of CEA fluctuate reflecting the number of malignant cells in the body it is usually measured throughout diagnostic, treatment and follow-up periods.
The test
A blood sample is taken from the vein by the means of venepuncture – hence, the blood is drawn from a vein usually on the forearm.
Later the sample is analysed by one of the methods:
- RIA (Radioimmunoassay);
- IRMA (Immunoradiometric assay);
- Centaur;
- ELISA;
It takes about 3 days to process the specimen.
Reference limits
- < or = 3 ng/L – is considered to be a normal level of CEA for non-smokers;
- <or = 5 ng/L – is considered to be a normal level of CEA for smokers;
- < 10 ng/L – a moderate increased CEA typical for smokers;
CEA in non-cancerous conditions
Some non-cancerous conditions are known to present with increased levels of CEA. Such conditions include lung diseases (emphysema), inflammatory bowel disease (ulcerative colitis), liver disease (alcoholic liver disease, obstructive jaundice, cirrhosis), peptic (stomach) ulcer, inflammation of the pancreas (pancreatitis), kidney disease and benign breast diseases.
CEA in colorectal (bowel) cancer
Significantly raised CEA levels at diagnosis of colorectal cancer warrants a worse prognosis and are at risk of disease relapse after treatment. After surgical removal of the tumour CEA levels decreases slowly within 6 weeks. If CEA levels are increased following the surgery and are not decreasing, it raises suspicion that some of the malignant tissues may still be present in the body, or it can be an early sign of the disease recurrence.
CEA should be continuously monitored after treatment completion as part of follow-up as if CEA levels start increasing disease recurrence is possible.
As for other cancer, the use of CEA as a tumour marker has not yet been fully established and is not currently recommended, although may be useful sometimes.