Cutaneous Leiomyosarcoma: A SEER Database Analysis, BACKGROUND Cutaneous leiomyosarcoma is a rare dermal neoplasm usually arising from the pilar smooth muscle. It is considered a relatively indolent neoplasm, and there is debate whether designation as sarcoma is appropriate. Owing to some conflicting data in the literature, however, its behavior warrants further clarification. OBJECTIVE To determine the clinical behavior and demographic and pathologic characteristics of cutaneous leiomyosarcoma. MATERIALS AND METHODS The Surveillance, Epidemiology and End Results database was used to collect data on cutaneous leiomyosarcoma and 2 reference populations: cutaneous angiosarcoma (aggressive) and atypical fibroxanthoma (indolent). Demographic and oncologic characteristics were examined, and overall survivals (OS) and disease-specific survivals were compared. RESULTS Leiomyosarcoma and atypical fibroxanthoma displayed lower stage (localized: 69.7% and 66.8% respectively), smaller size (<3 cm: 90.5% and 72%), and lower rates of disease-specific mortality (2.9% and 7.8%) compared with angiosarcoma. Patients with leiomyosarcoma had a 5-year disease-specific survival rate of 98% and OS rate of 85%. CONCLUSION Cutaneous leiomyosarcoma shows outcomes similar to atypical fibroxanthoma. It is nearly always indolent and should be distinguished from more aggressive cutaneous and subcutaneous sarcomas. Clear communication of the biologic potential may be best achieved using alternate diagnostic terminology such as “atypical intradermal smooth-muscle neoplasm.” Address correspondence and reprint requests to: Paul N. Bogner, MD, Departments of Pathology and Dermatology, Roswell Park Comprehensive Cancer Center, Elm and Carlton Streets, Buffalo, NY 14263, or e-mail: Paul.Bogner@roswellpark.org The authors have indicated no significant interest with commercial supporters. © 2019 by the American Society for Dermatologic Surgery, Inc. Published by Wolters Kluwer Health, Inc. All rights reserved.