Stereotactic ablative body radiotherapy (SABR) for bone only oligometastatic breast cancer: A prospective clinical trial

BACKGROUND: Stereotactic ablative body radiotherapy (SABR) is an emerging noninvasive approach for the treatment of oligometastases. Limited prospective evidence is available in breast cancer. OBJECTIVES: To determine the safety and feasibility of single fraction SABR for patients with bone only oligometastatic breast cancer. Secondary endpoints were local and distant progression-free survival (LPFS and DPFS), toxicity and response assessment. METHODS AND MATERIALS: In this single institution prospective trial we screened patients with computed tomography, bone scan, and sodium fluoride positron emission tomography. Eligible patients had one to three bone only oligometastases. All patients were treated at a dose of 20Gy in 1 fraction to each metastasis. Kaplan-Meier methods were used to determine local and distant progression free survival (LPFS and DPFS). Toxicity was graded using Common Terminology Criteria for Adverse Event version 4.0. RESULTS: 15 eligible patients were recruited to the study. Median follow-up time was 24 months. The treatment was feasible in 12 (80%) of patients with 3 (20%) of patients having treatment delayed by more than 3 days. 10 (67%) of patients experienced grade 1 treatment related toxicity, 4 (27%) experienced grade 2 toxicity and no patients experienced grade 3 or 4 treatment related toxicity. The two-year LPFS was 100%, DPFS was 67%. CONCLUSION: We observed that SABR is feasible, well tolerated and effective in this cohort with two thirds of patients disease-free at two years. In selected patients with bone-only oligometastatic disease, SABR could be considered a treatment option. Randomised trials are required to assess the impact of SABR on overall survival when compared to the standard of care.