Immunological relationship of the carcinoembryonic antigen and the fetal sulfoglycoprotein antigen

A simple immunological procedure was used for purification of CEA (carcinoembryonic antigen of colon cancer). Evidence is presented that CEA shares a common antigenic determinant with FSA (fetal sulfoglycoprotein antigen) of cancerous gastric juice. This determinant seems not to be identical with the true colon cancer specific antigen of the CEA macromolecule. Immunodiffusion data suggest the possibility that both determinants are to be found in the CEA macromolecule, while the colon cancer specific determinant is lacking in the FSA macromolecule. Unabsorbed anti-CEA contains antibodies to both determinants, the non-specific component can be removed only by an intensive absorption with colon tissue antigens, necessarily in particle form. The importance of the finding for the specificity of the radioimmunoassay of CEA is discussed.