Immunodiscrimination of colorectal neoplasia using MUC1 antibodies: Discrepant findings in tissue versus stool

Colorectal tumor-associated antigens are attractive targets for novel stool -screening assays. MUC1, a glycoprotein antigen, is aberrantly expressed in transformed colorectal mucosa and represents a candidate fecal biomarker. In this study, tissue staining and stool testing were performed to further clarify the discriminant potential of MUC1 in markedly different biologic m edia. One anti-MUC1 monoclonal antibody (MA5) was used for immunohistochemi stry and two commercially available MUC1 assay kits (ELSA-CA 15-3 and Truqu ant BR) were used for stool detection. On tissue staining, MUC1 expression was strong in 40/40 (100%) adenocarcinomas, moderate in 42/55 (76%) adenoma s, faint in 8/28 (29%) juxtatu-moral mucose specimens, and absent in 15/15 (0%) nonadjacent mucosa specimens. Conversely MUC1 levels in stool testing did not differ between colorectal cancer cases (N = 14) and controls (N = 1 4). Based on these results, MUC1 appears to be a functional tumor biomarker in colorectal tissue but not in stool. Bacterial metabolism within stool m ay unmask the core antigen of MUC1 and account for this discordance in immu noreactivity.