BACKGROUND: Population-based investigations of leiomyosarcoma (LMS) of the skin are limited; many studies of LMS have not stratified results by dermal versus subcutaneous origin of the tumor. OBJECTIVE: To characterize the incidence, tumor characteristics, and prognostic factors of skin primary LMS. METHODS: Retrospective population-based analysis of the 17 registries of the Surveillance, Epidemiology, and End Results Program (2000-2021). RESULTS: Dermally-based LMS (dLMS) has an incidence of 0.59 (95% CI, 0.56-0.63) cases per million person-years, whereas subcutis-based LMS (sLMS) has an incidence of 3.87 (95% CI, 3.78-3.96). Dermally-based LMS has a 5-year disease-specific survival (DSS) of 96.8% (95% CI, 95.7-98.0) whereas sLMS has a DSS of 62.9% (95% CI, 61.7-64.2). Advanced age, female sex, head and neck disease, distant stage at diagnosis, and income <$75,000 were associated with worse DSS for dLMS and sLMS. Tumor size and Fédération Nationale des Centres de Lutte Contre le Cancer grade 2/3 were observed to negatively affect DSS for sLMS but not dLMS. CONCLUSION: Dermally-based LMS generally has a favorable prognosis, whereas sLMS is characterized by a much more aggressive course. Advanced age, female sex, head and neck disease, and distant stage at diagnosis are high-risk features for both dLMS and sLMS.
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Joshi et al. (2025) studied this question.