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.