IMMUNOHISTOCHEMICAL DEMONSTRATION OF MYOEPITHELIAL CELLS IN SWEAT GLAND CARCINOMAS

Although myoepithelial cells are detectable in many benign sweat gland tumours, little is known about their role in sweat gland carcinomas. To specifically demonstrate myoepithelial cells, paraffin sections fro m 46 sweat gland carcinomas were stained, using a standard avidin-biot in-peroxidase complex method, with the monoclonal alpha-smooth muscle actin antibody 1A4. Myoepithelial cells were not found in adenoid cyst ic eccrine carcinoma (n=2), malignant nodular hidradenoma (n=2), poroc arcinoma (n=4), extramammary Paget's disease (n=12), sclerosing sweat duct carcinoma (n=4) or in adenosquamous-mucoepidermoid carcinoma (n=1 ). In contrast, myoepithelial cells were demonstrated in two of eight apocrine adenocarcinomas, one of six mucinous eccrine carcinomas and t wo of seven eccrine adenocarcinomas, In all these tumours myoepithelia l differentiation was found in peripheral cells of solid tumour island s, or in basal cells of tubular structures. However, in most areas of the tumours, myoepithelial layers were discontinuous. Cells in the cen tre of solid tumour nodules, and luminal cells of tubular structures, were negative for a-smooth muscle actin. In analogy to breast tumours, in which malignancy and invasiveness correlate with scattered or abse nt myoepithelial cells, we suggest that disrupted myoepithelial layers in sweat gland carcinomas may be interpreted as a loss of the invasio n barrier.