Immunohistochemistry with keratin, vimentin, desmin, and alpha-smooth muscle actin monoclonal antibodies in canine mammary gland: benign mammary tumours and duct ectasias.

Duct ectasias (n = 2) and different types of benign canine mammary tumours (n = 19) were studied immunohistochemically with monoclonal antibodies (MoAbs) directed against various human keratin types (K), alpha-smooth muscle actin, vimentin, and desmin. In the duct ectasias and in most tumours the epithelial structures revealed an inner and outer cell layer. The inner cell layer was characterized by labelling with K 7, 8, 18, 19 and mostly also with K 4 and/or K 10 MoAbs. The outer cell layer was almost invariably labelled by K 14, K 14 and 17, and a-smooth muscle actin MoAbs. The labelling patterns of both duct ectasias and tumours corresponded largely to the patterns observed in normal mammary gland tissue, although a more distinct heterogeneity was seen. Tumours histomorphologically assumed to be of a myoepithelial origin did not show immunohistochemical features of myoepithelial cells. The myoepithelial nature of the vast majority of spindle-shaped cells present in the adenomas of the complex type and in the fibroadenomas of the benign mixed type could not be confirmed immunohistochemically. These cells, however, unequivocally expressed vimentin, suggesting proliferation of stromal cells in these tumours, which in the fibroadenomas of the benign mixed type may show metaplasia to bone or cartilage. In the duct ectasias and in some tumours, a fraction of elongated stromal cells, probably representing myofibroblasts, was labelled with the alpha-smooth muscle actin MoAb.