Expression of beta-catenin, E-cadherin and APC in canine mammary tumors.

Background: Mammary tumors are a very common neoplasm in the dog and show histological features and biological behaviour similar to human mammary carcinomas. Recently, a pathway named Wnt-1, involving beta-catenin and APC protein, has emerged as an important player in many human tumor types, including mammary neoplasms. Materials and Methods: Thirty-five samples of canine mammary tumors (10 benign and 25 malignant) were studied in order to evaluate the co-expression of P-catenin, APC protein and E cadherin with confocal laser microscopical observation, by western blot analysis and by correlating data obtained with the histological grade of tumours. Results: A progressive decrease of E-cadherin together with disruption of P-catenin expression was observed in less differentiated malignant tumors. In addition, a loss of P-catenin membranous distribution and a cytoplasmic accumulation was often coexpressed with disrupted expression of APC protein. Western blot analysis showed a progressive increase of P-catenin in malignant tumors, which could be the expression of disrupted beta-catenin catabolism leading to cytoplasmic accumulation. In some less differentiated malignant tumors, a marked,beta-catenin decrease was also observed. This feature could be linked to mutations in P-catenin gene coding for a truncated and lighter protein. Conclusion: These results may indicate the multifunctional role played by P-catenin in canine mammary oncogenesis