Carcino Embryonic Antigen (CEA ) is a useful tumor marker. In particular it is useful in patients with adenocarcinomas. It has been reported to be raised in many different tumours. In particular it is increased in adenomcaricomas of the colon, breast, esophagus, stomach and ovary. In general a baseline CEA prior to resection is taken. If this is raised, it should fall to normal levels post resection. Then it should stay normal. If it increases it acts as a marker for subclinical recurrance and in general preceeds overt systemic disease by about 1 year. It has not been demonstrated that CEA assessment improves prognosis in colorectal cancer but many clinicians find it useful.
CEA is a glycoprotein that is not normally found in adult tissues. The only adult tissues known to express it are cancers. It is normally found in embryonic tissues, however, thus it is termed carcino embryonic antigen. Conceptually, re-expression of CEA in tumour tissue may represent reversal of the cells to a more primative type.
Of note if the the CEA level is normal pre op, then it is unlikely that it will be useful as a tumour marker in the post operative period. Smokers have a higher upper limit of CEA than non-smokers, so in following the result, you need to check to see the trend in the CEA and know whether the patient is a smoker or not.