CLEAR-CELL SMOOTH-MUSCLE TUMOR OF THE SKIN

We report a case of a previously undescribed benign neoplasm character ized by a poorly circumscribed proliferation of clear cells, arranged both singly and in elongated fascicles oriented in haphazard fashion w ithin the middle and lower reticular dermis, The fascicles consisted o f spindle-shaped cells that were periodic acid-Schiff positive and dia stase labile, These cells were characterized by oval, hyperchromatic, cigar-shaped nuclei and clear cytoplasm. Immunohistochemically, neopla stic cells were diffusely positive for smooth muscle actin (1A4), comm on muscle actin (HHF-35), and vimentin, Immunoreactivity for fibronect in was also focally noted. The neoplasm, which we designated clear-cel l smooth muscle tumor of the skin, should be distinguished from smooth muscle hamartoma and other smooth muscle proliferations at cutaneous level, We highlight in this case report the histopathologic differenti al diagnosis among other tumors with myofibroblastic, melanocytic, and neural differentiation.