Stereotactic Body Radiotherapy in Oligomestatic/Oligoprogressive Sarcoma: Safety and Effectiveness Beyond Intrinsic Radiosensitivity

Background: Metastatic soft tissue sarcoma (STS) patients may benefit from local ablative treatments due to modest efficacy of systemic chemotherapy. However, use of stereotactic body radiotherapy (SBRT) is controversial because of presumed radioresistance of STS. Methods: Patients treated with SBRT for oligometastatic and oligoprogressive metastatic STS were retrospectively reviewed to assess results in terms of local control (LC), disease-free survival (DFS), and overall survival (OS). Incidence and grade of adverse events were reported. Statistical analysis was performed to identify variables correlated with outcome and toxicity. Results: Forty patients were treated with SBRT to a median biologic effective dose (BED) of 105 (66-305) Gy5 to 77 metastases. Two-year LC, DFS, and OS were 67%, 23%, and 40%. Improved LC was shown in patients receiving a BED >150 Gy5 (hazard ratio [HR], 3.9; 95% confidence interval [CI], 1.6-9.7; P = 0.028). A delay >24 months between primary tumor diagnosis and onset of metastases was associated with improved DFS (HR, 0.46; 95% CI, 0.22-0.96; P = 0.01) and OS (HR, 0.48; 95% CI, 0.23-0.99; P = 0.03). No toxicity grade ≥3 was observed. Conclusions: Stereotactic body radiotherapy is effective in metastatic STS with a benign toxicity profile. A BED >150 Gy5 is required to maximize tumor control rates. Metastatic relapse >24 months after diagnosis is correlated to improved survival.