OPTIMAL / stereotactic radiotherapy SABR-COMET: What the Cancer Trial Found

An old assumption, questioned

For decades, cancer that had spread was treated as one thing. Once it was in more than one place, treatment aimed to slow it and ease symptoms, not to remove it.

The oligometastatic idea challenges that. Oligo means few. The proposal is that some people have only a handful of secondary tumors, and that treating every one of them might change how long they live. The word for taking that seriously is not optimism. It is a testable claim.

SABR-COMET tested it.

What the treatment is

Stereotactic ablative radiotherapy, or SABR, delivers a very high radiation dose to a small, precisely mapped target over a handful of sessions. It is the same idea as stereotactic body radiotherapy, and it is aimed at destroying a tumor rather than easing a symptom.

Because the dose is high and the target is tight, it can be used on spots in the lung, liver, bone, or elsewhere without a major operation. Our page on radiation therapy covers how planning and delivery work.

How the trial was built

The trial ran at 10 hospitals in Canada, the Netherlands, Scotland, and Australia. It enrolled 99 people between February 2012 and August 2016.

To take part, a person needed a primary tumor that was under control and one to five metastatic lesions. They also had to be reasonably well, with an ECOG performance score of 0 or 1, and a life expectancy of at least six months.

Assignment was 1 to 2. Thirty-three people received standard palliative care alone. Sixty-six received the same care plus SABR to every metastasis. The commonest primary cancers were breast, lung, colorectal, and prostate.

One design detail matters. This was a randomized phase 2 screening trial, and the authors set the threshold for a positive result at p below 0.20 rather than the usual 0.05. That is a deliberately loose bar, chosen to decide whether a bigger trial is worth running. Our explainer on clinical trial phases sets out what each phase is designed to answer.

What it found

Median overall survival was 41 months in the SABR group against 28 months in the control group. The hazard ratio was 0.57, and the p-value was 0.090. Under the trial's own rule, that counted as positive.

Under the conventional 0.05 threshold, it would not have. Both statements are true at once, and holding both is the honest reading.

The five-year picture

The team published long-term results in 2020, with a median follow-up of 51 months. Those numbers were stronger.

Five-year overall survival was 42.3 percent in the SABR group against 17.7 percent in the control group, with a stratified log-rank p-value of 0.006. Five-year progression-free survival was 17.3 percent with SABR against 3.2 percent at four years in the control group. The authors reported no new grade 2 to 5 adverse events and no difference in quality of life between the groups.

The effect grew rather than faded. In a small trial, that is the pattern you want to see.

The harm column

This is not a free intervention.

Adverse events of grade 2 or worse occurred in 3 of 33 controls, or 9 percent, and in 19 of 66 people given SABR, or 29 percent. That is an absolute increase of 20 percentage points.

More seriously, three of the 66 people in the SABR group, or 4.5 percent, had a treatment-related death. There were none in the control group. The trial's own conclusion names that figure alongside the survival benefit.

What the authors themselves called for

The published interpretation is direct. SABR was associated with improved overall survival and met the trial's primary endpoint, and 4.5 percent of the SABR group died of treatment. Phase 3 trials are needed to show an overall survival benefit conclusively, and to work out the maximum number of metastatic lesions for which SABR helps.

That last question is unresolved. The trial stratified people by whether they had one to three lesions or four to five, and 99 people is too few to answer where the line falls. Our page on metastatic cancer explains what spread means in the first place.

What this trial cannot tell you

• This was phase 2, with 99 people and a deliberately relaxed statistical threshold. It was designed to justify a larger trial, not to end the question.
• Everyone enrolled was well, with a controlled primary tumor and few metastases. Most people with metastatic cancer do not fit that description.
• The primary cancers were mixed. The trial cannot say which cancer types benefit most.
• A 4.5 percent treatment-related death rate is part of the result, not a footnote to it. Any discussion of this approach has to include it.

Sources

• Palma DA, et al., Lancet 2019 — SABR-COMET abstract via NCBI E-utilities
• Palma DA, et al., J Clin Oncol 2020 — SABR-COMET long-term results via NCBI E-utilities
• ClinicalTrials.gov API v2 record for NCT01446744
• NCI: What Is Cancer?

How this page was made

An AI-assisted editorial system helped prepare this page. This article has not been reviewed by a healthcare professional unless a named reviewer is specifically shown. Cancer Explained is published by the National Cancer Information Foundation as a nonprofit-oriented public-interest education project. It is not a diagnostic service, does not recommend treatments, and is not for emergencies.

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