Limited improvement of tumour diagnosis by the simultaneous determination of carcinoembryonic antigen (CEA) and of a tumour-associated CEA-related antigen of Mr 128,000 in serum.

Two biotin-avidin based enzyme immunoassays were developed using three monoclonal anti-CEA antibodies with distinct epitope- and antigen-specificities. A broadly cross-reactive monoclonal anti-CEA antibody (T84.1) was immobilized on a solid support. Either monoclonal antibody T84.66 or CEA.11 was used as the second, biotin-labeled monoclonal antibody. Both antibodies do not cross-react with normal granulocytes or bile canaliculi. Monoclonal antibody CEA.11 binds to CEA and to an antigen with a relative molecular mass of 128,000 present in extracts from solid carcinomas. Monoclonal antibody T84.66 does not cross-react with the antigen of Mr 128,000. After adsorption of tumour extracts to a CEA-specific immunosorbent, residual activity was measurable by the CEA.11 assay, but not by the T84.66 assay. Serum samples (n = 726) from patients with malignant and non-malignant disease, as well as from healthy volunteers, were analysed by both immunoassays and by two commercial CEA immunoassays. In comparison with the T84.66 assay and the commercial assays, the CEA.11 assay did not significantly increase the sensitivity or specificity of tumour diagnosis.