SABR-COMET: Stereotactic Ablative Radiotherapy vs Standard Palliative Treatment in Oligometastatic Cancers


Key Points

  • SABR was associated with improved overall survival vs standard of care palliative treatment.
  • Three treatment-related deaths occurred in the SABR group.  

Results of the phase II SABR-COMET trial reported by Palma et al in The Lancet indicate that stereotactic ablative radiotherapy (SABR) was associated with improved survival vs standard palliative treatment in patients with oligometastatic cancers, although it was also associated with treatment-related deaths.

Study Details

The open-label trial included 99 patients with a controlled primary tumor and 1 to 5 metastatic lesions from 10 hospitals in Canada, the Netherlands, Scotland, and Australia. Primary tumors included breast, colorectal, lung, prostate, and others. Most patients (93%–94%) had 1 to 3 metastases.

Patients were randomly assigned 2:1 between February 2012 and August 2016 to standard of care plus SABR to all metastatic lesions (n = 66) or to standard of care palliative treatment, including palliative radiation therapy (n = 33).

The primary endpoint was overall survival in the intent-to-treat population. A randomized phase II screening design was used with a two-sided α of 0.20 (P < .20 indicates a positive trial).

Overall Survival

Median follow-up was 25 to 26 months. Median overall survival was 41 months (95% confidence interval [CI] = 26 months–not reached) in the SABR group vs 28 months (95% CI = 19–33 months) in the control group (hazard ratio = 0.57, P = .090). Two (3%) patients in the SABR group did not receive study treatment and withdrew from the trial, and two (6%) in the control group withdrew from the trial. Median progression-free survival was 12.0 months vs 6.0 months (HR = 0.47, P = .0012).

Adverse Events

Treatment-related adverse events of grade ≥ 2 occurred in 29% of the SABR group vs 9% of the control group (P = .026), with the most common in the SABR group being fatigue (n = 4), dyspnea (n = 2), and pain (n = 8, including muscle, bone, and other pain). Three treatment-related deaths occurred in the SABR group (4.5%), consisting of death due to radiation pneumonitis, pulmonary abscess, and subdural hemorrhage after surgery to repair a SABR-related perforated gastric ulcer. No treatment-related deaths were observed in the control group.

The investigators concluded, “SABR was associated with an improvement in overall survival, meeting the primary endpoint of this trial, but 3 (4.5%) of 66 patients in the SABR group had treatment-related death. Phase III trials are needed to conclusively show an overall survival benefit and to determine the maximum number of metastatic lesions wherein SABR provides a benefit.”

David Palma, MD, of London Health Sciences Centre, London, Ontario, is the corresponding author for The Lancet article.

Disclosure: The study was funded by Ontario Institute for Cancer Research and London (Canada) Regional Cancer Program Catalyst Grant. For full disclosures of the study authors, visit

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