Diagnostic significance of the myoepithelial cells in the benign and malignant sweat gland tumors.

We studied the presence of myoepithelial cells (MCs) in the benign and malignant sweat gland adenomas by immunostaining with antibody to alpha-smooth muscle actin. We found peripheral arrangement of MCs in the neoplastic nests in cutaneous cylindromas (9), spiradenomas (13), syringoadenomas (7), and one case of adenoid cystic carcinoma. Dispersed MCs were identified in some cases of nodular hidradenoma (7/13) and malignant portion of spiradenocarcinoma (2/3). The remnants of the peripheral arrangement of MCs were retained in the benign part in cylindrocarcinoma and every case of spiradenocarcinoma, likewise in composed malignant adnexoma (malignisation within cylindroma/spiradenoma). We could not find MCs in papillary eccrine adenoma (2), poromas (7) and porocarcinomas (3), syringomas (6), chondroid syringomas (3), malignant nodular hidradenoma (1) and malignant portion of syringoadenoma (1). In one of three cases of eccrine hidradenocarcinoma focal myoepithelial differentiation could be identified at the periphery of the epithelial nests. These results confirm heterogeneity of the differentiation in sweat gland tumors, emphasizing the validity of division of those tumors into those with the differentiation towards secretory and ductal portion of the gland. The former group demonstrates the variability of arrangement of myoepithelial cells depending on the degree of dedifferentiation of the developing carcinoma. These cells may be replaced by outgrowing tumor, but may also accompany the neoplastic growth. Less significant is the presence of the MCs in the adenomas with ductal differentiation, which either in benign and malignant tumors may be lacking. The variability of MCs occurrence in cutaneous adenomas and carcinomas precludes its significance as a solitary factor in the differentiation between benign and malignant proliferations.