How useful is carcinoembryonic antigen in detecting colorectal malignancy?

Abstract

Carcinoembryonic antigen (CEA) is one of the most widely used tumour markers worldwide, mostly in relation to tumours of epithelial origin especially colorectal adenocarcinoma. The molecular biology is that of a high molecular weight glycoprotein (180–200 kDa), involved in cell adhesion, innate immunity and apoptosis. Its chemical structure is based on a variable carbohydrate moiety and two immunoglobulin (Ig) domains, the Ig variable domain (IgV-like) and the Ig constant domain (IgC2-like). It is linked to cell membranes via a glycosylphosphatidylinositol anchor, with a soluble form available with phospholipase C or D. It is expressed in foetal development and by normal colonic mucosa (50–70 mg/day), most of which is evacuated in faeces. In malignant processes CEA is hypothesised to accelerate progress to metastatic disease through its involvement in cellular adhesion. Unfortunately, a common practice in everyday clinical medicine is the use of CEA by physicians and general practitioners to look for colorectal carcinoma (CRC) (outside of a screening programme) in patients with non-specific gastrointestinal symptoms.