LAUSR

e23526 Background: Leiomyosarcoma is a rare malignancy that may occur in bone. This investigation described the characteristics and outcomes of primary leiomyosarcoma of bone (PLB) compared to soft tissue leiomyosarcoma (SLMS). Methods: This study was a retrospective review using the Surveillance, Epidemiology, and End Results (SEER) database from 1975 to 2016. Continuous and categorial variables were described, and Cox regression were used to identify factors of prognostic significance. Results: Seven thousand five-hundred two patients met inclusion criteria. Seventy-four (1%) were PLB and 7428 (99%) were SLMS. On multivariable analysis for high-grade SLMS radiation (neoadjuvant: HR, 0.56; 95% CI, 0.4-0.8; p = 0.003, and adjuvant: HR, 0.75; 95% CI, 0.6-0.9; p = 0.008) and surgery (procedure specific) improved DSS, while age (HR, 1.013; 95% CI, 1.0-1.1; p < 0.001), tumor size greater than or equal to 5 cm (HR, 3.16; 95% CI, 2.3-4.2; p < 0.001), abdomen/pelvis/trunk/thorax tumors (HR, 1.31; 95% CI, 1.1-1.6; p = 0.006), and distant metastases at presentation (HR, 2.6; 95% CI, 2.1-3.3; p < 0.001) negatively influenced DSS. Conclusions: Radiation and surgery positively influence survival in high-grade SLMS while chemotherapy appears to have no benefit. Surgery alone appears to lower the mortality risk in PLB.