211 - Treatment with Stereotactic Ablative Radiotherapy for up to Five Oligometastases in Patients with Cancer: Long-Term Outcomes of the Nonrandomized Phase 2 SABR-5 Clinical Trial
Presenter(s)
C. T. Leclerc1, S. Baker2, W. Jiang3, B. Mou4, M. Liu5, A. Bergman6, D. Schellenberg2, A. S. Alexander7, H. Carolan6, N. Chng8, Q. Matthews1, A. Benny1, S. Tyldesley6, and R. A. Olson9; 1University of British Columbia, Vancouver, BC, Canada, 2BC Cancer Surrey, Surrey, BC, Canada, 3BC Cancer - Surrey, Surrey, BC, Canada, 4BC Cancer, Kelowna, BC, Canada, 5BC Cancer Vancouver, Vancouver, BC, Canada, 6BC Cancer - Vancouver, Vancouver, BC, Canada, 7BC Cancer, Victoria, BC, Canada, 8BC Cancer, Prince George, BC, Canada, 9BCCA - Prince George, Prince George, BC, Canada
Purpose/Objective(s): Despite the growing use of SABR for oligometastatic cancer, prospective data on long-term survival outcomes remain limited. This study evaluated the long-term secondary trial endpoints of overall survival (OS), progression-free survival (PFS), local control rate, and prognostic factors in the population-based phase 2 SABR-5 trial.
Materials/Methods: The SABR-5 trial was a single-arm phase 2 study with the primary endpoint of toxicity, conducted at the 6 regional cancer centers across British Columbia (BC), Canada, during which time SABR for oligometastases was only offered on trial. Patients with up to 5 oligometastases (total or not controlled by prior treatment and including induced oligometastatic disease) underwent SABR to all lesions. Patients were 18 years of age or older, had an Eastern Cooperative Oncology Group (ECOG) score of 0 to 2, and had life expectancy = 6 months.
Results: Between November 2016 and July 2020, 380 patients underwent SABR on trial. The 3 most common histologies were prostate (32.1%), colorectal (16.6%), and breast (11.1%). Most patients had 1-2 metastatic lesions (90.5%) treated. Median follow-up was 54.2 months (interquartile range, 29.3 - 60.4). Median OS was 64.6 months (95% confidence interval [CI], 61.0-68.1). Median PFS was 14.6 months (CI, 11.6-17.6). 5 -year OS, PFS, and local control were 58.6% (CI, 53.5 - 63.7), 20.3% (CI, 16.2 - 24.4), and 85.1% (CI, 82.0-88.1) respectively. On multivariable analysis, ECOG =1 (Hazard Ratio [HR], 1.53; p = 0.01), tumour diameter (HR, 1.13; p <.001), colorectal histology (HR, 2.25; p = 0.008), lung histology (HR, 4.25; p<.001), 1-2 treated lesions (HR, 2.17; p = 0.021), no upfront systemic therapy (HR, 1.79; p = 0.032) and no synchronous oligometastatic disease (HR, 1.56; p = 0.04) were significant independent predictors of worse OS. ECOG =1 (HR, 1.33; p = 0.019), tumour diameter (HR, 1.10; p<.001), no upfront systemic therapy (HR, 1.61; p = 0.009), oligoprogression (HR, 1.53; p = 0.010), and metachronous disease (HR, 1.47; p = 0.014) were associated with worse PFS.
Conclusion: In this large population-based cohort consisting of genuine oligometastatic, oligoprogressive, and induced oligometastatic disease, the median OS and PFS were 64.6 months and 14.6 months, respectively. The favorable OS and PFS may suggest a role for SABR beyond the genuine oligometastatic paradigm and highlight the potential benefit of durable local tumor control in this patient population.