Cutaneous myoepithelioma arising within hidradenoma of the scalp.

A 62-year-old man presented with a 2-year history of a 2-cm cystic mass involving his occiput. There had been recent enlargement, and the clinical impression was that of a pilar cyst. Histopathological sections showed a partially dermal solid and cystic proliferation. The tumor contained areas of glandular differentiation with cuboidal to columnar cells lining luminal and cystic spaces. A concurrent spindle cell proliferation was seen interspersed between glands and also formed broad, cellular sheets of cells. The stroma was sclerotic and without chondroid or myxoid elements. Immunohistochemistry showed that the spindled cells expressed S100 protein, cytokeratin and smooth muscle myosin. The immunohistochemical profile and the relationship with ductal elements supported myoepithelial differentiation. The proliferation warranted the diagnosis of myoepithelioma arising from a hidradenoma, which to our knowledge has not been previously described. In addition to discussing this case, we provide a brief review of epithelial-myoepithelial neoplasms encountered in the skin.