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Primary cutaneous myoepitheliomas are rare tumors composed of sheets and islands of various proportions of spindle, plasmacytoid, epithelioid, and clear cells that exhibit myoepithelial differentiation. Only one case of soft tissue myoepithelioma involving masticator space has been reported in Korea so far. We report a case involving the subcutis of the sole. A 37-year old woman presented with an incidentally found palpable mass in her left sole. Grossly, the tumor was well-circumscribed and measured 2.2 cm in greatest dimension. The cut surface showed tan ovoid mass with firm consistency. Histological examination revealed an encapsulated tumor composed exclusively of plasmacytoid cells in the myxoid stroma. In some areas, the tumor cells demonstrated mixed arrangement with reticular areas merging into the solid areas. Inother areas, there were trabecular growth pattern. A small number of cytologically atypical large cells were seen, with irregular, occasionally multiple nuclei with smudged chromatin, and frequent nuclear pseudoinclusions and distinct nucleoli. Occasional mitotic figures were present but a formal mitotic count was less than 1 mitosis per 10 high power field. Immunohistochemistry revealed diffuse strong positive staining with S100 protein, vimentin and pancytokeratin. There was focal staining with epithelial membrane antigen and smooth muscle actin, but no staining with c-kit and CD34. Occurring in unusual location, myoepithelioma should be still considered in the differential diagnosis as a primary cutaneous or soft tissue tumor.
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