(P 238) EPIDEMIOLOGIC SURVEY OF MYXOFIBROSARCOM USING DATA FROM THE BONE AND SOFT TISSUE TUMOR REGISTRY IN JAPAN

Objective: Myxofibrosarcoma is a common sarcoma among older patients, with locally infiltrative behavior and a predilection for local postoperative recurrence. Some studies have reported the factors affecting prognosis, although only a few have mentioned the previous staging classification systems. This study investigated the clinical overview and prognosis of myxofibrosarcoma to determine the optimal treatment.

Methods: This retrospective study analyzed the records of 349 patients with myxofibrosarcoma in the nationwide Bone and Soft Tissue Tumor Registry in Japan from 2006 to 2015. Clinical features, treatment options, and patient outcomes were investigated.

Results: Ultimately, 349 patients were identified. The overall survival rates were 93.1% at 2 years and 84.3% at 5 years. A multivariate analysis was performed using the Cox proportional hazards model. The study identified four sig- nificant prognostic factors for survival: tumor size, depth, compartment status, and location. The prognostic score was calculated by summing the scores of all the factors. The overall survival rate was 69.3% at 5 years for the patients with prognostic scores of 6 or higher. Conversely, the patients with prognostic scores of 2 or lower had a survival rate of 95.6% at 5 years.

Conclusion: Among myxofibrosarcomas, those larger than 5 cm, deep-seated, invaded into the external compartment, or in axial body parts were associated with a significantly worse prognosis. Adjuvant radiotherapy and chemotherapy did not contribute significantly to a better prognosis. Previous staging classification systems are impractical for prognosis prediction. Therefore, new classifications are needed. Further research on new treatment methods for patients with a poor prognosis will be crucial in the future.