Syringoid eccrine carcinoma: report of a case with immunohistochemical analysis of cytokeratin expression.

Syringoid eccrine carcinoma is an extremely rare cutaneous malignant tumor, thought to be derived from eccrine sweat apparatus. We report a case of syringoid eccrine carcinoma occurring on the scalp of a 66-year-old woman and analyzed its cytokeratin expression immunohistochemically to clarify its histogenesis. The tumor consisted mainly of numerous small cords and nests extending from the reticular dermis to the subcutaneous tissue, which formed luminal or tubular structures mimicking the nests of syringoma. Immunohistochemical analysis revealed that most tumor cells expressed simple epithelial cytokeratins (CKs 7, 8, 18, 19) suggesting their sweat secretory differentiation, and that a small number of tumor cells showed an expression of stratified epithelial cytokeratins (CKs 5, 14) suggesting their ductal differentiation. We believe that the syringoid eccrine carcinoma of our case may differentiate mainly toward the sweat secretory cells rather than toward the dermal ductal cells.