Treatment With Stereotactic Ablative Radiation Therapy for Patients With up to 5 Oligometastatic Cancer Lesions: Long-Term Outcomes of the Nonrandomized Population-based Phase 2 SABR-5 Clinical Trial.

Abstract

The use of SABR for oligometastatic cancer is expanding, but prospective long-term survival data are limited. This study reports long-term secondary outcomes of overall survival (OS), progression-free survival (PFS), local control, and prognostic factors from the population-based phase 2 SABR-5 trial. The SABR-5 trial was a single-arm phase 2 study with the primary endpoint of toxicity, conducted across 6 regional cancer centers in British Columbia, Canada. Eligible patients had ≤5 oligometastases (new or uncontrolled by prior therapy, including induced oligometastatic disease), were ≥18 years of age with ECOG performance status 0-2, and had a life expectancy ≥6 months. All lesions were treated with SABR. From November 2016 to July 2020, 380 patients were treated. The most common histologies were prostate (32.1%), colorectal (16.6%), and breast (11.1%). Most patients (90.5%) had 1-2 lesions. Median follow-up was 54.2 months. Median OS was 64.6 months (95% CI, 61.0-68.1) and median PFS was 14.6 months (95% CI, 11.6-17.6). Five-year OS, PFS, and local control were 58.6% (95% CI, 53.5-63.7), 20.3% (95% CI, 16.2-24.4), and 85.1% (95% CI, 82.0-88.1), respectively. On multivariable analysis, worse OS was independently associated with ECOG ≥1, larger tumor diameter, colorectal or lung histology, 1-2 lesions, no upfront systemic therapy, and absence of synchronous oligometastatic disease. Predictors of worse PFS included ECOG ≥1, larger tumor diameter, no upfront systemic therapy, oligoprogression, and metachronous disease. 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, highlighting the potential benefit of durable local tumor control in this patient population.