e21502 Background: Leiomyosarcoma (LMS) of bone is a very rare sarcoma subtype. These tumors are managed akin to osteosarcoma, with neoadjuvant chemotherapy followed by surgery. The precise role of chemotherapy remains to be defined. Methods: Patients treated with primary bone LMS at the University of Washington between 2002 and 2012 were included. Patients with high grade tumors were treated with neoadjuvant chemotherapy and surgery; whereas those with low grade tumors were treated with surgical resection alone. Chemotherapy consisted of doxorubicin and ifosfamide x 2 cycles. Treatment details included: initial treatment (surgery versus chemo), surgical and pathological margins, and timing of chemotherapy. Follow-up data included: time to local recurrence, time to metastasis, time to last follow up if alive, or time to death. Results: Ten patients were identified, 4 male and 6 female. Median age at diagnosis: 52 years (range 29 - 91). The primary site was the distal femur in 5 patients, and the hemipelvis, acetabulum, proximal femur, distal clavicle and mid-shaft of femur in 1 patient each. Median tumor size at diagnosis was 8 cm. Five were high-grade tumors; 3 were intermediate and 2 were low grade. Four of 10 patients received neoadjuvant chemotherapy, with the following histological response; 70%, 30%, 15% and <5%. None of these patients had a dimensional radiological response to chemotherapy. Of the patients treated with surgery alone, one developed a local recurrence and another developed metastatic disease. Of the patients treated with chemotherapy and surgery, 1 died from an unrelated cause. Median follow-up was 9 months (range 0 - 83). Median DFS was 9 months (range 0 - 83). OS has not yet been reached. Conclusions: Surgical resection remains the mainstay of management of LMS of bone. The role of neoadjuvant chemotherapy requires further evaluation. Larger collaborative studies and biomarker analyses are essential to evaluate optimal treatment strategies for this rare disease.