(P 374) DISTINCT PATTERNS OF METASTATIC SPREAD IN LEIOMYOSARCOMA: A COMPARATIVE ANALYSIS OF TRUNCAL AND EXTREMITY TUMOURS

Objective: Leiomyosarcoma (LMS) is a soft tissue sarcoma (STS) with a potentially distinct metastatic pattern compared to other sarcomas. This study evaluates the distribution and frequency of metastases in truncal and extremity LMS, hypothesizing a higher rate of extra-pulmonary spread relative to other STS.

Methods: A retrospective cohort analysis of patients undergoing truncal and extremity LMS resections from 1995–2022, compared to a cohort of non-LMS STS patients. Benign tumors and STS subtypes predisposed to extra-pulmonary metastases, including myxoid liposarcoma, were excluded. Baseline demographic and tumor variables, metastatic rates, and anatomical distribution were compared. Overall (OS) and disease-free survival (DFS) were assessed using Kaplan-Meier curves.

Results: There were 354 LMS and 1,141 non-LMS STS patients. Age and sex distributions were comparable, but LMS patients were more likely to present with low-grade (p < 0.001), superficial tumors (p < 0.001). The overall rate of metastases was similar (28% LMS vs. 26% non-LMS). However, LMS was associated with a significantly higher rate of extra-pulmonary metastases (29% vs. 15%, p< 0.006), with soft tissues, viscera, and lymph nodes being the most common sites. LMS patients exhibited superior 5-year DFS compared to non-LMS patients (72% vs. 66%, p=0.018), while 5-year OS rates were similar (77% vs. 74%).

Conclusion: LMS demonstrates a distinct metastatic profile, with a higher incidence of extra-pulmonary metastases compared to other STS. These findings suggest the potential benefit of refined surveillance approaches to account for the unique metastatic behavior of LMS.