[Carcinofetal antigens. II. Carcinoembryonic antigen (CEA). (author's transl)]

CEA is a beta1-glycoprotein (mol. w. approx. 200 000) which in embryonic life is usually found as a cell membrane associated antigen in the gastrointestinal (GI) tract and pancreas. Furthermore, it is secreted into body fluids. In healthy adults a very low serum concentration may be found. The clinical significance of CEA lies in its increased formation in primary and secondary adenocarcinomas of colon and rectum and pancreatic carcinoma, where values of 20 ng/ml and more are observed. However, other gastrointestinal (e.g. oesophagus, stomach, gall-bladder) and extragastrointestinal tumors (e.g. lung, breast, urogenital, prostatic, ovarial carcinomas) as well as non-malignant diseases mainly of the GI tract (e.g. hepatitis, cirrhosis, pancreatitis, colitis, diverticulitis) may provoke less frequent and lower increases in the CEA level. Healthy smokers also tend to show a slight increase in CEA concentration. A certain relationship exists between the CEA level and the size and extent of the tumor so that a decrease following operation may account for complete tumor removal, whereas a persistent or recurring increase in the CEA level is highly suspicious of metastases and/or recurrent tumor. Difficulties in proving and purifying CEA are mainly caused by multiple cross-reactions of CEA with other substances, e.g. blood group substances (A, B, Lea, Leb) and normal or other antigens (NGP, NCA, CEX, CCEA 2, NCA 2, CCA-III, FSA, BCGP). The radioimmunoassay is the most suitable method to determine CEA levels in body fluids. The 3 procedures used differ in the precipitation of the specific immune complex by ammonium sulphate (AS), Z-gel (ZG) or a second antibody (SA). Depending on the method, the upper normal limit in serum or plasma corresponds to approximately 2.5 (AS, ZG) or 12.5 (SA) nanogramme/milliliter. CEA determination in the urine is of interest in patients suffering from bladder carcinoma.