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There is a lack of long-term randomized data assessing the impact of ablative therapies in patients with oligometastases. The SABR-COMET randomized phase II trial was originally designed with 5 years of follow-up, but in light of better-than-expected survival outcomes, the trial was amended in 2016 to extend follow-up to 10 years. Herein we report oncologic outcomes beyond 5 years.

We enrolled patients with a controlled primary tumour and up to five metastatic lesions, with all sites of disease amenable to stereotactic ablative radiotherapy (SABR). Patients were randomized in a 1:2 ratio between palliative standard of care (SOC) treatment (control arm) vs. SABR to all metastases plus SOC (SABR arm). The primary endpoint was overall survival (OS) and secondary endpoints included progression-free survival (PFS), toxicity, quality of life (QOL, using the FACT-G), and time to new metastases. This analysis took place in January 2022, after 5 years of minimum potential follow-up in all patients.

Ninety-nine patients were randomized between 2012-2016 (n=33 in Arm 1 vs. n=66 in Arm 2). Primary tumour sites included lung (n=18), breast (n=18), colon (n=18), prostate (n=16), and other (n=29). Median age was 68 years and most were male (60%). Eight-year OS was 27.2% in the SABR arm vs. 13.6% in the control arm (HR: 0.50, 95% CI: 0.30-0.84; stratified log-rank p=0.008). 8-year PFS estimates were 21.3% vs. 0%, respectively (HR: 0.45, 95% CI: 0.28-0.72; p < 0.001). Rates of grade ≥ 2 acute or late toxicities were 30.3 vs. 9.1% respectively (p=0.019), most commonly fatigue and pain, with no new grade 3-5 toxicities. There was no difference between arms in the cumulative incidence of new metastases (stratified Gray’s p=0.46). FACT-G QOL scores declined over time in both arms, but there were no differences in QOL scores between arms. The use of systemic therapy overall was similar between arms, but patients in the SABR arm were less likely to require cytotoxic chemotherapy (33% vs. 55% respectively, p=0.043). Of the 25 patients in the SABR arm alive beyond 5 years, 11 had no progression events since SABR, and 5 others required salvage SABR at some point after randomization.

SABR achieved durable improvements in OS and PFS, with no new major toxicity signals with extended follow-up. A minority of patients randomized to the SABR arm (1-in-6) achieved > 5 years of survival without recurrence. Ongoing imaging follow-up after SABR is warranted to detect salvageable recurrences.