[526] Immunoreactivity of Smoothelin in Skin and Superficial Soft Tissue Tumors and Reactive Proliferations

S Loghavi, M Sandoval, BL Balzer. Cedar-Sinai Medical Center, Los Angeles, CA

Background: The role of this study was to investigate the expression pattern of Smoothelin, a marker protein for contractile smooth muscle cells, in skin and soft tissue spindle cell proliferations, compare it to expression in the normal structures of skin and evaluate its possible role in the separation of true smooth muscle neoplasms from their mimics.
Design: A total of 43 cases with either myofibroblastic, fibroblastic, true smooth muscle, or glomus differentiation were examined by H&E and classified as follows: Dermatofibroma (5), Dermatofibrosarcoma protuberans (3), cutaneous leiomyoma (9), pilar leiomyosarcoma (3), glomus tumor (4), nodular fasciitis (3), hypertrophic scar (4), fibromatosis (5), oral fibroma (4), malignant fibrous histiocytoma (3). In addition, 6 cases of surgically removed unremarkable skin were used as normal controls. The scoring of Smoothelin reactivity was as follows: 3+ (strong cytoplasmic reactivity in >10% of cells), 2+ (moderate reactivity in >10% of cells), 1+ (weak reactivity in >10% of cells).
Results: Smoothelin reactivity was only expressed in true smooth muscle tumors and normal structures composed of true smooth muscle. It was consistently present in a 3+ pattern in the erector pili muscles and media of arteries in normal skin. All leiomyomas were Smoothelin positive (1+ to 3+ patterns). Two of three leiomyosarcomas were positive (1+ to 2+ patterns). All other cases were negative for Smoothelin.
Conclusions: Our results demonstrate that Smoothelin expression in the skin and soft tissue is limited to structures and neoplasms composed of true smooth muscle. This is analogous to the pattern of reactivity seen in other anatomic sites such as the bladder and gastrointestinal tract. It therefore can be used to distinguish true smooth muscle neoplasms from their mimics.
Category: Dermatopathology

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 102, Wednesday Afternoon


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