Carcinoembryonic antigen

Carcinoembryonic antigen (CEA), described by Gold and Freedman in 1965, was the first and most widely used plasma tumor marker. Like AFP, it belongs to the so-called 'oncofetal' antigens, which are normally found in fetal tissues and plasma but are present only in very small quantities in normal adult subjects.

It has been shown that CEA consists of a group of proteins of between 175 and 200 kDa, containing up to 50% carbohydrate, whose immune reactivity resides on the protein moieties. Early studies suggested that high levels of CEA are produced by fetal colon and colon carcinoma cells and that only small amounts of CEA are present in plasma from normal adult subjects (upper limit between 5 and 20ngml"'; subsequent investigations have shown that abnormally high levels of CEA are also produced in patients with primary and secondary can cers of the liver, breast and ovarian rumors, and occasionally in patients with acute or chronic hepatic disease. Modest elevation of CEA has been detected in patients with colitis.

The general view is that CEA tests display adequate sensitivity but very poor specificity, and thus plasma estimation of this antigen is of little value in screening high-risk groups or asymptomatic individuals. Adding to the clinical problems, there are also technical difficulties associated with the immunologic techniques employed to estimate CEA plasma levels owing to interassay variability.

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