Stereotactic Ablative Radiotherapy for the Comprehensive Treatment of Oligometastatic Cancers: Long-Term Results of the SABR-COMET Phase II Randomized Trial

Abstract Purpose The oligometastatic paradigm hypothesizes that patients with a limited number of metastases may achieve long-term disease control, or even cure, if all sites of disease can be ablated. However, long-term randomized data testing this paradigm are lacking. Methods We enrolled patients with a controlled primary malignancy and 1-5 metastatic lesions, with all metastases amenable to stereotactic ablative radiotherapy (SABR). We stratified by the number of metastases (1-3 vs. 4-5) and randomized in a 1:2 ratio between palliative standard of care (SOC) treatments (Arm 1) vs. SOC plus SABR (Arm 2). We employed a randomized phase II screening design with a primary endpoint of overall survival (OS), using an alpha of 0.20 (wherein a p-value <0.20 indicates a positive trial). Secondary endpoints included progression-free survival (PFS), toxicity, and quality of life (QOL). Herein we present long-term outcomes from the trial. Results Between 2012 and 2016, 99 patients were randomized (33 in Arm 1, 66 in Arm 2) at 10 centres internationally. Median age was 68 (range 43-89) and the majority (n=59; 60%) were male. The most common primary tumor types were breast (n=18), lung (n=18), colorectal (n=18), and prostate (n=16). Median follow-up was 51 months. Five-year OS was 17.7% in Arm 1 (95% confidence interval [CI]: 6-34%) vs. 42.3% in Arm 2 (95% CI: 28-56%; stratified log-rank p=0.006). Five-year PFS was ‘not reached’ in Arm 1 (3.2% [95% CI: 0-14%] at 4-years with last patient censored) and was 17.3% (95% CI: 8-30%) in Arm 2 (p=0.001). There were no new grade 2-5 adverse events and no differences in QOL between arms. Conclusions With extended follow-up, the impact of SABR on OS was larger in magnitude than in the initial analysis, and durable over time. There were no new safety signals, and SABR had no detrimental impact on QOL. ( NCT01446744 ) Funding Ontario Institute for Cancer Research and London Regional Cancer Program Catalyst Grant