1. Zoe Ryan Carcinoembryonic Antigen (CEA)

2. What is CEA? Carcinoembryonic antigen is a protein found in the blood of some adults who have certain cancers mainly cancer of the large intestine. CEA is normally produced during the development of the foetus and production stops prior to birth, and is not usually found in the blood of a healthy adult. Because CEA can be found in trace amounts in some normal adults, its presence is not necessarily diagnostic tumours but can be used to monitor tumour growth.

3. History of CEA It was identified in 1964, by Gold and Friedman. Initially CEA was not thought to be found in normal colonic epithelium but was found in embryonic gut. After more sensitive monoclonal antibodies were developed, CEA was found in the normal colon and many other tumours as well as colon cancer. After research, the findings of CEA are characteristic of many tumour-associated antigens, eg. CA-125, MUC-1

4. Link to diseases It can be used as a tumour marker in clinical tests due to serum levels being raised in patients with certain cancers. Raised CEA levels are also found in patients with alcoholic hepatitis, biliary obstruction, chronic heavy smokers and other conditions.

5. Tests Blood Test: CEA levels are tested by carrying out a blood test. AccuBind ELISA is an immunoassay that is used to test the level of CEA in a blood sample as seen in figure 1. It can also be tested in bodily fluids and in biopsy tissue.

6. AccuBind ELISA High affinity and specificity antibodies with different epitope recognition are required for this immunoassay. A monoclonal antibody, an enzyme antibody and a serum containing the native antigen and antibodies are mixed forming a complex. The antibody-bound fraction is separated from the unbound antigen. Enzyme activity found in the antibody bound fraction is directly proportional to the native antigen concentration. Different serum references of known antigen values cam be compared to the values obtained.

7. Overview of CEA The main use of CEA is as a tumour marker, especially with intestinal cancer. It is useful in monitoring the treatment of CEA rich tumours. If CEA is high prior to treatment, it should fall to normal after successful therapy. A rising CEA level indicates progression or recurrence of the cancer. Certain benign conditions that can increase CEA include smoking, infection, inflammatory bowel disease, pancreatitis and some benign tumours.

8. References Carcinoembryonic Antigen (CEA). 2016. Carcinoembryonic Antigen (CEA). [ONLINE] Available at:http://www.webmd.com/cancer/carcinoembryonic-antigen-cea. [Accessed 10 February 2016]http://www.webmd.com/cancer/carcinoembryonic-antigen-cea Lee P, Jain S, Bowne WB, Pincus MR, McPHerson RA. Diagnosis and management of cancer using serologic and tissue tumour markers. In: McPherson RA, Pincus MR, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Philadelphia, Pa: Elsevier Saunders; 2011:chap 73. CEA blood test: MedlinePlus Medical Encyclopedia. 2016. CEA blood test: MedlinePlus Medical Encyclopedia. [ONLINE] Available at: https://www.nlm.nih.gov/medlineplus/ency/article/003574.htm. [Accessed 12 February 2016]https://www.nlm.nih.gov/medlineplus/ency/article/003574.htm Castellucci, DT et al., 2005. Professional Guide to Diagnostic Tests. 1st ed. USA: Lippincott Williams & Wilkins. Pp 338,339,467-470 Macdonald, F, 2000. Professional Guide to Diagnostic Tests. 2nd ed. UK: Bios Scientific Publishers. Pp 137,166,168,179 Mendelsohn, Gray, Howley, 2015. The Molecular Basis of Cancer. 4th ed. Philadelphia: Elsevier Saunders. Pp329-330