Objective:

To identify risk factors that enable stratification of patients with dermal leiomyosarcoma (dLMS) into high-risk and low-risk groups.

Approach:

• Study Design: A nationwide cohort study was conducted using data from the Danish National Health Registers, including the Danish National Pathology Register and the National Patient Register, covering patients diagnosed with dLMS from 1980 to 2022.
• Data Collection: Patient and tumor characteristics were collected, including age, sex, tumor location, margin status, tumor diameter, invasion depth, and presence of necrosis or infiltration.
• Tumor Classification: Tumors were classified according to WHO guidelines and included both dLMS and atypical intradermal smooth muscle neoplasms (AISMN).
• Outcome Definitions: Local recurrence and metastasis were defined based on specific diagnostic codes and clinical criteria.
• Statistical Analysis: Baseline characteristics were summarized, and patients were followed until emigration, death, or the end of the study period.

Key Findings:

• Dermal leiomyosarcoma (dLMS) is classified as an intermediate-risk neoplasm with a considerable risk of local recurrence but a low risk of metastasis.
• No significant difference in metastasis risk was found between atypical intradermal smooth muscle neoplasms (AISMN) and dLMS.
• Current studies on risk factors for dLMS have been limited by small sample sizes and short follow-up periods.

Interpretation:

The study highlights the need for further investigation into risk factors for dLMS metastasis and local recurrence, as existing classifications are not validated for cutaneous sarcomas.

Limitations:

• Limited by the retrospective nature of the study and reliance on national health registers.
• Potential misclassification of tumors despite manual review of pathology reports.

Conclusion:

Further research is necessary to establish validated risk classifications for dermal leiomyosarcoma.