Bone metastasis in extremity soft tissue sarcomas: risk factors and survival analysis using the SEER registry.

INTRODUCTION While lung is the most common site of metastasis, bone metastasis of soft tissue sarcoma is a part of the natural history affecting the prognosis of these patients. To date, no studies have analyzed the histologic subtypes more likely to metastasize to bone, the risk factors for bone metastasis at initial presentation, or the effect that bone metastasis has on the survival of these patients. MATERIAL/METHODS Patients were identified from the Surveillance, Epidemiology and End Results database with primary extremity STS between 2010 and 2015. Risk factors for early bone metastasis, survival based on different sites of metastasis, and prognostic factors of survival were analyzed. RESULTS Among 8,234 STS, 2.2% (n = 180) presented with skeletal metastasis. Bone metastasis was more likely when regional lymph nodes were involved (OR = 4.48, p = 0.008). Deep and moderate or high-grade sarcomas had 5-12-fold tendency to present with bone and lung metastasis (p = 0.046, 0.006, 0.030, respectively). The 5-year survival rate was 41.2% (26.9-54.9%) for isolated bone metastasis and 32.9% (21.2-45.1%) for patients with bone and lung metastasis. Resection of the primary sarcoma was the only significant predictor of survival (HR = 0.44, p = 0.021) for patients with bone metastasis. CONCLUSION High tumor grade, deep location to fascia and regional lymph node metastasis are significant risk factors for skeletal metastasis at diagnosis of an extremity STS. While neither systemic chemotherapy nor radiotherapy of the primary sarcoma has a significant influence on survival in the presence of bone metastasis, radical resection of the primary STS is associated with increased survival.