Comparison of serological expression of different epitopes on the CA50-carrying antigen CanAg

C203 and C242 are mouse monoclonal antibodies (MAbs) generated using a human colon carcinoma cell line. They recognize novel tumour-associated epitopes present in elevated levels in sera from patients with colon and pancreatic cancer. These epitopes were found to be co-expressed with sialylated Lewisa on the CanAg molecule. To study the association and distribution of the epitopes of CanAg in sera, these new antibodies, together with C50, were used in different combinations in time-resolved fluoroimmunoassays. Relative serum concentrations were examined in patients with various types of carcinoma and in patients with ulcerative colitis and benign pancreatic, and hepatobiliary diseases. A double-determinant assay using C50 and C242 was shown to distinguish carcinoma from benign biliary and hepatocellular diseases better than a single-determinant assay based on C50 as both catching and tracing antibody. The number of sera with elevated CanAg levels from patients with benign obstructive biliary disease was 17 out of 29 using the single-determinant CA50 assay. This was reduced to 4 out of 29 in the double-determinant assay. When sera from patients with liver cirrhosis were analyzed, 16 of 23 patients showed elevated CanAg levels with the C50-C50 combination, but only 4 of 23 patients had elevated antigen values using the C50-C242 assay. The increased specificity was obtained without loss of sensitivity. MAb C203 was evaluated both in a double-determinant combination with C50 and in an homologous assay, but did not contribute either increased sensitivity or specificity as compared with C50-C50.