Stereotactic body radiotherapy in oligomestatic/oligoprogressive sarcoma: Safety and effectiveness beyond intrinsic radiosensitivity.

Background: Soft tissue sarcomas (STS) are a group of rare, heterogeneous tumors. Scarce terapeuthic options are currently available, given the limited efficacy of systemic chemotherapy. Patients with low-burden metastatic disease may benefit from adjunction of local ablative treatments. However, because of the presumed radioresistance of STS, stereotactic body radiotherapy (SBRT) has not been steadily considered as a viable treatment option. Methods: We retrospectively reviewed STS patients treated with SBRT in a single institution,, for oligometastatic and oligoprogressive metastatic disease. Local control (LC), disease-free survival (DFS), and overall survival (OS) were assessed. We also reported the incidence of early and late adverse events and their grade according to Common Terminology Criteria for Adverse Events (CTCAE) 5.0. Univariate and multivariate statistical analysis were carried out to investigate variables correlated with outcome and toxicity. Results: Forty patients were treated between 2012 and 2019 to 77 metastases with SBRT to a median biologic effective dose (BED5, assuming an α/β=5) of 105 Gy (range 66 to 305 Gy). 63% of patients had received 2 or more chemotherapy lines at the time of SBRT. LC, DFS and OS at two years were 67%, 23% and 40% respectively. At multivariate analysis, LC only significantly improved in patients receving a BED5>150 Gy (hazard ratio [HR] 3.9. 95% confidence interval [CI], 1.6-9.7; p=0.028), while an interval>24 months between primary tumor diagnosis and metastatic disease relapse was correlated with improved DFS and OS (HR, 0.46; 95% CI, 0.22-0.96; P = 0.01 and HR, 0.48; 95% CI, 0.23- 0.99; P = 0.03, respectively). Early toxicity was observed in 4 patients, late toxicity in 1 patient. No toxicity grade>2 was observed. Conclusions: SBRT is an effective therapeutic option in metastatic STS. A BED5>150 Gy5 is required to obtain better tumor control rates. Metastatic relapse>24 months after diagnosis is correlated with improved overall survival. Adverse events are scarce and mostly transient, meaning SBRT is safe and could be an option even in heavily pretreated patients. [ABSTRACT FROM AUTHOR]