Immunohistochemical characterization of canine intestinal epithelial and mesenchymal tumours with a monoclonal antibody to hepatocyte paraffin 1 (Hep Par 1).

Monoclonal antibody hepatocyte paraffin 1 (Hep Par 1) is reported to be highly specific and sensitive for hepatocellular tumours of humans and dogs. However, in a previous study we observed immunoreactivity for Hep Par 1 in an intestinal adenocarcinoma metastatic to the liver. In this paper, we examined normal intestine and 57 canine intestinal tumours including adenocarcinomas of the small and large intestine, colonorectal polyps, mucinous carcinomas, stromal tumours, leiomyosarcomas, fibrosarcoma, plasmacytomas, and osteosarcoma for immunoreactivity for Hep Par 1. Normal intestinal epithelial cells were strongly labelled, particularly at the base of crypts. However, epithelial cells in small intestinal neoplasms had variable reactivity for Hep Par 1. In contrast, normal colonic epithelium was seldom labelled, but hyperplastic or neoplastic colonic epithelium was usually reactive to Hep Par 1. Five of seven small intestinal adenocarcinomas, two of three large intestinal adenocarcinomas, two of three mucinous adenocarcinomas, and all (29) rectal polyps were positive for Hep Par 1. The staining was diffuse, granular and cytoplasmic. The only non-epithelial tumours positive for Hep Par 1 were two of four leiomyosarcomas. Hep Par 1 can be used to differentiate hepatocellular from biliary neoplasms but its value in differentiating metastatic tumours to the liver is questionable due to the reactivity of Hep Par 1 in many intestinal tumours.