Cutaneous myoepithelioma - An under-recognized cutaneous neoplasm composedof myoepithelial cells

Benign and malignant neoplasms of myoepithelial cells comprise a rare but w ell-characterized group of tumors, among which myoepithelioma of the saliva ry glands is the best known. Extrasalivary examples of myoepithelioma also have been described in the breast, larynx, and retroperitoneum. Recently, m yoepithelioma of the soft tissue also has been reported. According to this description, myoepithelioma and mixed tumors arising in the skin and subcut is represent points along a clinicopathologic spectrum of cutaneous and sof t-tissue tumors. To the best of our knowledge, there has been only one case report of an entirely cutaneous myoepithelioma in the literature We report herein five additional examples of purely myoepithelial tumors located exc lusively in the dermis. Histopathologically, the neoplasms were well-circum scribed dermal lesions composed of fascicles of spindle cells with eosinoph ilic cytoplasm and ovoid- to spindle shaped nuclei. Focally, neoplastic agg regations of more epithelioid cells representing large round cells with abu ndant pare cytoplasm arranged in solid clusters, cords, or strands were als o seen. Ductal differentiation was not identified in either of these solid aggregations of epithelioid cells or in the fascicles of spindle-shaped cel ls. Nuclear pleomorphism in epithelioid and spindle-cell areas was mild, an d mitotic figures were very sparse. In some eases, small, necrotic areas we re seen within the solid aggregations of spindle-shaped cells. Neoplastic s troma was scant and composed of fibrillary collagen and abundant mucin. Tn one case, the stroma consisted of clusters of mature adipocytes intermingle d with fascicles of myoepithelial cells. Areas of chondroid or osteoid meta plasia were not seen in any of the cases. Immunohistochemically, neoplastic cells expressed positivity for muscle specific actin (HHF35), alpha smooth muscle actin (IA4), S-100 protein, glial fibrillary acidic protein (GFAP), and epithelial membrane antigen (EMA), whereas stains for pan-cytokeratin (MNF116) were focal and weak. The findings in this report expand the clinic al and histopathologic spectrum of cutaneous myoepithelioma, an under-recog nized cutaneous neoplasm of myoepithelial cells.