[CEA and related antigens as possible new tumor markers]

Although carcinoembryonic antigen (CEA) is a well established tumor marker and being applied widely to many clinical fields, it still possesses many unclear problems in its chemical and physicochemical properties, antigenic structure and assay systems. There exist some possibilities that the unclear problems concerning CEA could be solved by establishment of some novel tumor marker systems which will be derived from the original CEA system. There are several CEA-related normal antigens; nonspecific cross-reacting antigen (NCA) from normal lung or spleen, NCA-2 from meconium, normal fecal antigen (NFA) from normal adult feces, which consists of 3 molecular species; NFA-1, NFA-2 and NFCA, and biliary glycoprotein I (BGP-I) from bile. As the results of antigenic analyses of CEA and these related antigens, it has been concluded that a CEA molecule can be divided into 4 antigenic moieties; NCA-common, NFCA-common, NFA-1-common, and CEA-distinctive moieties. Since none of CEA assay systems available at present detects the CEA-distinctive moiety, a system which can detect the CEA molecule by this distinctive antigenic moiety must be a very important and novel tumor marker system. Since all of CEA assay systems at present measured CEA and NFA-2 simultaneously, an assay system for NFA-2 in sera must be quite useful for establishing the serum concentration of CEA proper. NFA-1 is a small molecular size antigen (M.W. 20,000) and retains major antigenic activity of the CEA molecule; therefore, NFA-1 would be applicable for establishing a unique CEA assay system which has equal reactivity to every CEA molecule in various malignant conditions. Synthetic peptides having the same amino acid sequences NH2-terminal portion of CEA may have some possibilities as a novel tumor marker. In all cases mentioned above, monoclonal antibodies to respective determinants must be essential and promising reagents for establishing assay systems of novel tumor markers.