Classification of High- and Low-Risk Patients With Dermal Leiomyosarcoma: An Exploratory Nationwide Cohort Study

Background: Risk factors for dermal leiomyosarcoma (dLMS) metastasis remain poorly defined because methodological constraints, small sample sizes, and short follow-up have limited previous studies. Objectives: To investigate risk factors for metastasis and local recurrence, and to propose a high- and low-risk classification for dLMS. Methods: All patients diagnosed with dLMS in Denmark between 1980 and 2022 were included. Absolute 5‑year risks were estimated using the Aalen-Johansen method, treating all‑cause mortality as a competing risk. Results: Among 381 patients (median age 66 years, 71% male), the 5-year risk of metastasis was 2.4% and 10% for local recurrence. The most important risk factors for metastasis were tumor necrosis, mitotic grade 3, and perineural/intravascular invasion, with 5-year absolute risks ranging between 9% and 25%. Positive surgical margins and perineural/intravascular invasion were associated with increased 5-year absolute risks of local recurrence, ranging between 26% and 50%. Conclusion: Although few distant metastases were observed, high-risk dLMS features may include tumor necrosis, mitotic grade 3, perineural/intravascular invasion, or positive surgical margins. Cases without these features may be classified as low-risk dLMS. We propose regular cross-sectional imaging in the follow-up of patients with high-risk dLMS, whereas follow-up for patients with low-risk dLMS could be limited to clinical examinations.