A direct assay for carcinoembryonic antigen in serum and its diagnostic value in metastatic breast cancer.

The development of an optimized direct assay for carcinoembryonic antigen (CEA) in serum is described. CEA was purified from liver metastases from colorectal carcinomas, and avid anti-CEA antibodies (Ka 1.0-1.6x10(11) L/mol) were produced in rabbits. Radiolabelling of CEA was performed by the "Iodo-Gen" method. Experiments performed in order to characterize antigen-antibody specificity and to work out assay conditions are described. In the separation step of the assay, problems associated with non-specific binding of radioligand were virtually eliminated by using a new solid-phase second antibody, based on monodisperse polymer particles. The clinical performance of the assay is demonstrated by its high ability to detect relapses in patients with mammary carcinoma.