Expression of CD44 in canine mammary tumours.

CD44 is an important adhesion molecule for hyaluronan, a major component of the extracellular matrix (ECM). In human breast cancer, the interaction of tumour cells with the ECM via CD44 is favoured as a major candidate for tumour progression and metastasis. The present study was designed to investigate immunohistochemically the expression of the standard form of CD44 in normal, hyperplastic and neoplastic canine mammary tissue. CD44 was expressed in normal and hyperplastic mammary tissue predominantly by ductal and alveolar epithelial cells and to a minor extent by myoepithelial cells. Stromal cells and blood vessels displayed low to moderate CD44 expression. In simple and complex adenomas and benign mixed tumours there was significant up-regulation of CD44 expression in alveolar epithelial cells compared with adjacent non-neoplastic mammary tissue. Peripheral epithelial cells of simple and complex adenomas, benign mixed tumours and complex carcinomas expressed significantly more CD44 compared with adjacent non-neoplastic mammary tissue. Peripheral epithelial cells of simple adenomas revealed a significantly higher CD44 expression compared with simple carcinomas. A statistical trend to greater CD44 expression was found in peripheral epithelial cells of complex adenomas, benign mixed tumours and complex carcinomas compared with simple carcinomas. Up-regulation of CD44 therefore appears to be associated with benign or relatively benign biological behaviour of canine mammary tumours.