Dysregulation of beta-catenin is common in canine sporadic colorectal tumors.

Human colorectal tumorigenesis is often initiated by APC (adenomatous polyposis coli) or beta-catenin (CTNNB1) mutations, which result in dysregulation of beta-catenin expression, followed by alterations in E-cadherin and/or p53. We examined 32 canine intestinal tumors for expression and intracellular distribution of beta-catenin, E-cadherin, and p53 using immunohistochemistry. beta-Catenin in normal mucosal epithelial cells was restricted to lateral cell membranes, but 13/13 (100%) colorectal adenomas had intense cytoplasmic and/or nuclear reactivity. Three of six (50%) colorectal carcinomas, 2/13 (15%) small intestinal carcinomas, and dysplastic cells in 1/2 focal hyperplastic lesions in the small intestine had a similar pattern of staining; remaining tumors had normal membranous beta-catenin reactivity. There was a correlation (P = 0.007) between abnormal beta-catenin and E-cadherin staining with 11/13 (85%) colorectal adenomas, 3/6 (50%) colorectal carcinomas, and 3/13 (23%) small intestinal carcinomas showing decreased membranous reactivity compared with normal mucosal epithelium. E-cadherin staining was reduced more often in adenomas than in carcinomas (P = 0.04). There were two patterns of nuclear p53 staining: > 60% of nuclei in 2/26 (8%) carcinomas (one colorectal, one small intestinal) were strongly labeled, whereas three colorectal adenomas and one small intestinal carcinoma had fainter staining in 10-20% of cells. Dysregulation of beta-catenin appears to be as important in canine colorectal tumorigenesis as it is in the human disease and could be due to analogous mutations. Malignant progression in canine intestinal tumors does not appear to be dependent on loss of E-cadherin or beta-catenin expression or strongly associated with overexpression of nuclear CMI antibody-reactivity p53.