Stereotactic ablative radiotherapy (SABR) for oligometastatic cancer is associated with improved overall and progression-free survival, new findings suggest.
In a randomized, open-label, controlled phase 2 trial involving 99 patients with up to 5 metastatic lesions, median overall survival 41 months among patients who underwent SABR compared with 28 months for control patients who received standard of care palliative treatment, David A. Palma, MD, of London Health Sciences Centre in London, Ontario, and colleagues reported in The Lancet. Median progression-free survival was 12 months in the SABR group compared with 6 months in the control arm.
SABR was associated with a nonsignificant 43% decreased risk of all-cause mortality and a significant 53% decreased risk of progression.
“Although further trials are needed,” Dr Palma’s team wrote, “the emerging evidence supports the existence of an oligometastatic state, and that patients with a limited number of metastases might be amenable to curative-intent treatment strategies.”
Investigators randomly assigned 66 (67%) patients to undergo SABR and 33 (33%) to the control group. The median follow-up was 26 months in the SABR group and 25 months in the control arm. Two patients in the SABR group and 2 in the control group withdrew from the trial.
Adverse events of grade 2 or worse occurred in 19 (29%) of SABR recipients and 3 (9%) controls. Treatment-related deaths occurred in 3 (4.5%) of the SABR group and none of the controls. The deaths occurred despite stringent dose constraints and a requirement for peer review of all radiation plans, according to the investigators. This finding suggests that SABR delivery should continue to focus on minimization of toxicity and that SABR use in patients with more than 5 lesions should be done in the context of a clinical trial, they stated.
Progression events occurred in 67 patients: 39 (59%) in the SABR group and 28 (85%) in the control arm.
The study population included patients with primary prostate (16 patients), breast (18 patients), colorectal (18 patients), lung (18 patients), and other cancers (29 patients). The lung was the most frequent site of metastases, followed by bone, liver, adrenal gland, and other sites (eg, brain, lymph nodes).
Palma DA, Olson R, Harrow S, et al. Stereotactic ablative radiotherapy versus standard of care palliative treatment in patients with oligometastatic cancers (SABR-COMET): a randomised, phase 2 open-label trial. Lancet. 2019;393:2051-2058.