E-cadherin immunoreactivity in canine mammary samples

The reduction or loss of E-cadherin, a calcium-dependent epithelial cell adhesion molecule, has been associated with tumor dedifferentiation and invasiveness. The immunohistochemical pattern of E-cadherin expression was evaluated in formalin-fixed and paraffin-embedded sections of 6 normal mammary glands, 3 dysplasias, 12 benign tumors (8 benign mixed tumors, 4 adenomas) and 60 malignant tumors (12 stage 0, 29 stage I, 19 stage II) of the canine mammary gland. E-cadherin expression was classified as membranous, when on cell-cell boundaries, or cytoplasmic, in form of a diffuse cytoplasmic staining. In addition, the percentage of E-cadherin positive epithelial neoplastic cells was graded by a semi-quantitative method, collecting cases in a so called Reduced (or -) type group, when showing less than 25% positivity, a Reduced (or +/-) type group showing 25-75% positivity, and Preserved (or +) type for more than 75% of positive cells. In the normal mammary gland E-cadherin expression was evident in epithelial luminal cells. A stronger positivity was revealed in ductular than in alveolar luminal cells. The myoepithelial cells showed inconstant weak cytoplasmic positivity in the normal gland as well as in mammary tumors. In normal glands, benign and malignant non-invasive tumors, E-cadherin expression was mainly membranous and preserved in most of the epithelial cells. In stage I tumors, both membranous (38%) and cytoplasmic (62%) positivity were well represented, as well as Preserved type (55%) and Reduced type (45%) tumors. All stage II malignant tumors showed the highest frequency of cytoplasmic positivity (79%) and Reduced type (62%) tumors.