Initial treatment modality and recurrence in non-metastatic leiomyosarcoma: A retrospective cohort study.

e23555 Background: Leiomyosarcoma (LMS) is an aggressive malignancy comprising 10–20% of soft tissue sarcomas, with high recurrence rates in non-metastatic cases. While surgery remains the mainstay, systemic therapy and radiation are often used for large, high-grade, or locally advanced tumors. Guidelines recommend neoadjuvant or adjuvant therapy in select non-metastatic cases, but how initial treatment influences recurrence remains unclear. We aimed to evaluate recurrence patterns by first treatment by analyzing real world data. Methods: We retrospectively reviewed non-metastatic LMS cases treated at the University of Miami. Patients were categorized by initial treatment: surgery, systemic therapy, or radiation. The primary outcome was recurrence (local or distant). Logistic regression was used to estimate odds of recurrence across treatment types. This project is part of an ongoing study that will further assess planned vs unplanned surgeries and high-risk features (e.g., high grade, large size) in systemically treated non-metastatic patients. Results: Among 151 patients, recurrence occurred in 58.1% of those receiving surgery first, 45.8% of those receiving systemic therapy first, and 50.0% of those receiving radiation first. Compared to the reference group, patients treated with systemic therapy first had significantly reduced odds of recurrence (OR 0.35, 95% CI 0.13–0.87, p=0.03). Although there was a trend toward higher recurrence odds with surgery first, the odds of recurrence were not statistically different in the surgery (OR 2.08, p=0.08) or radiation (OR 1.71, p=0.54) first groups. Conclusions: Systemic therapy as the initial treatment was significantly associated with lower odds of recurrence for patients with non-metastatic LMS. These findings support further investigation into treatment sequencing and highlight the importance of tailoring therapy based on risk features. Using real world data we can design investigator initiated trials to further validate findings and improve care in LMS.