Maspin expression in myoepithelial tumors of the breast

Maspin is a mammary inhibitory serine protease that harbors tumor suppressor, tumor invasiveness-suppression and anti-angiogenic properties. It is consistently expressed by mammary myoepithelial cells. However, to the best of our knowledge, no assessment of maspin immunoexpression in myoepithelial cell lesions of the breast has been reported so far. We evaluated maspin expression by immunohistochemistry in five normal breast samples, one sclerosing papilloma (SP), one tubular adenomyoepithelioma (TA), one adenoid cystic carcinoma (ACC), one epithelial-myoepithelial carcinoma of the breast (EMC), and one malignant adenomyoepithelioma (MA). We also compared maspin expression with the expression of other classic myoepithelial markers in myoepithelial and secretory cells, as well as in stromal components of all samples. In normal breast samples, maspin expression was restricted to myoepithelial cell nuclei and cytoplasm. A strong nuclear and cytoplasmic maspin immunoreactivity was observed in the myoepithelial components of SP, TA, ACC, and EMC. In MA, maspin immunoreactivity was confined to the nucleus and cytoplasm of the cells lining tubular-like and papillary structures, as well as in squamous cells. The myoepithelial nature of maspin-positive cells was further confirmed by classic myoepithelial cell markers, including alpha-actin and S-100 protein. No stromal, neural or vascular components were immunostained by maspin. In spite of the small number of myoepithelial lesions here assessed, we suggest that maspin should be used in surgical pathology practice either as an additional marker in immunohistochemical panels defining a myoepithelial histogenesis in odd breast neoplasms, or in those cases in which the definite diagnosis relies on the myoepithelial cell layer identification.