2018 ASTRO: SABR-COMET: Stereotactic Ablative Radiation Therapy for Oligometastatic Tumors


Key Points

  • Median overall survival was 41 months for patients treated with SABR compared to 28 months in the standard treatment arm.
  • Progression-free survival was 12 months in the stereotactic radiation arm compared to 6 months for those who received standard radiation therapy.
  • Just 9% of patients who received standard treatments experienced serious adverse events (grade 2 or higher), while 30% of those in the SABR arm did.

In the first randomized, phase II clinical trial of its kind, researchers have shown that an aggressive form of high-precision radiation therapy can increase survival in patients with oligometastatic tumors. These findings were presented by Palma et al in the plenary session at the 60th Annual Meeting of the American Society for Radiation Oncology (ASTRO) and published in the International Journal of Radiation Oncology • Biology • Physics.

The multicenter trial studied patients with a variety of oligometastatic cancers, treating them with stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiation therapy (SBRT), which is a form of high-precision cancer therapy that delivers substantially higher doses of radiation to the tumor site in just one or a few treatment sessions.

“Traditionally, when a patient had a cancer that spread to other parts of their body—such as to their bones or brain—they were considered to be incurable,” said lead study author David Palma, MD, PhD, a researcher at Lawson Health Research Institute, the research institute of London Health Sciences Centre, in a statement. “But there’s a theory—called the oligometastatic theory—that if a patient only has a few spots of cancer returning, those spots could be killed with radiation or surgery to improve their survival. Now, we’ve been able to show, for the first time in a randomized trial, that high-dose radiation can effectively treat these limited recurrences, and we’ve been able to increase survival by a median of 13 months.”


In this randomized, phase II, open-label study called SABR-COMET, Dr. Palma and his colleagues enrolled 99 patients from four countries (Canada, Scotland, the Netherlands, and Australia). Each patient had been treated for cancer but the cancer had returned, with tumors appearing in as many as five different places. All patients had good performance status (ECOG 0–1) and a life expectancy of more than 6 months. Patients had been diagnosed with a wide range of cancer types, most commonly breast, lung, colorectal, and prostate. In most patients (n = 92), the cancer had spread to one to three new sites.

Between February 2012 and August 2016, the patients were randomly assigned at a 1:2 ratio into two treatment arms: palliative standard of care treatments (SOC), and SOC plus stereotactic radiation therapy for all metastatic lesions. The median patient age was 68 years (range = 43–89), and 59% of the patients were male. No baseline patient characteristics were significantly different between the two treatment arms. Median follow-up time was 27 months.


Median overall survival was 41 months (95% confidence interval [CI] = 26 months, upper limit not reached) for patients treated with SABR compared to 28 months (95% CI = 19–33 months) in the standard treatment arm (stratified log rank P = .09). This phase II trial was designed to look for a signal, defined as a P value less than .20, as an initial comparison of these two treatment groups.

Progression-free survival was 12 months (95% CI = 6.9–30 months) in the stereotactic radiation arm compared to 6 months (95% CI = 3.4–7.1 months) for those who received standard radiation therapy (P = 0.001).

“We were surprised and quite pleased. We didn’t expect survival benefit to be quite so long for patients with metastatic disease,” said Dr. Palma, also a clinician-scientist at the Ontario Institute for Cancer Research.

Adverse Events

Being treated with stereotactic radiation resulted in more negative side effects than standard treatments. Just 9% of patients who received standard treatments experienced serious adverse events (grade 2 or higher), while 30% of those in the SABR arm did (P = .022). The most common negative side effects were fatigue, dyspnea, muscle and joint pain, bone pain, or pain not otherwise specified. Three patients in the experimental arm died due to adverse events—one from a pulmonary abscess; one from subdural hemorrhage after surgery to repair a SABR-related perforated gastric ulcer, and one from radiation pneumonitis.

“Stereotactic radiation therapy needs to be delivered carefully and by an experienced team, and there is a small risk of very serious side effects, as well as mortality. But overall, for patients whose cancers have spread, and who are not expected to survive otherwise, the overall survival benefit of SABR appear to outweigh these risks,” said Dr. Palma.

There were no differences between the two treatment arms in quality of life measures. Scores on the Functional Assessment of Cancer Therapy: General (FACT-G) questionnaire at 6 months following treatment were similarly high for both patient groups (82.5 for SABR vs 82.6 for standard therapy, P = .992). Patients also reported similar quality of life outcomes on the physical, social, functional and emotional FACT-G subscales (all P > .4).


In some cases, patients developed additional lesions during the trial. When this happened, noted Dr. Palma, the additional tumors could sometimes be successfully ablated. Because they were able to successfully treat a greater number of sites in these patients, the research team is now planning a follow-up study that will enroll patients with up to 10 metastatic lesions, called SABR-COMET-10.

“We don’t know the upward limit of how many tumors can be treated with SABR,” he said. “The concern is the amount of radiation exposure a patient can tolerate. We don’t know yet what the safe boundaries are. We’ve been very conservative, as this is a new technology.”

Nearly half (46%) of the patients treated with stereotactic radiation were still alive after 5 years, compared to 24% in the control group, said Dr. Palma—a result that he believes will encourage physicians to consider SABR as a treatment option.

“Ultimately, the question of whether an oncologist will offer this treatment as the standard of care for [patients with oligometastatic disease] will be up to that oncologist,” he said. “At the very least, physicians should be considering this as a treatment option for their patients.”

“Stereotactic radiation therapy can increase how long these patients live and how long they live without their cancer coming back, and it doesn’t seem to have a detrimental impact on their quality of life,” he concluded.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.