Gastrointestinal cancer-associated antigen in immunoperoxidase assay.

A monosialoganglioside antigen of gastrointestinal adenocarcinomas defined by murine monoclonal antibody was demonstrated by immunoperoxidase (IP) assay in fixed paraffin-embedded tumors in 59% of colonic adenocarcinomas, 86% of pancreatic adenocarcinomas, and 89% of all gastric adenocarcinomas. In all patients with detectable levels of antigen in circulation, the resected tumors also expressed the antigen in IP assay. Six of eight individuals with no detectable levels of antigen in their serum samples expressed the antigen in the tumor tissue. Removal of the sialic acid residue of the antigen abolished the IP reaction. The successful use of the IP assay on fixed tissue to demonstrate the specific sites of gastrointestinal cancer antigen localization in human tumors and normal tissues provides an important tool for the study of developing neoplasia.