Stereotactic ablative radiotherapy may improve survival of patients with metastatic disease. In a phase II trial, patients with a small number of metastases due to breast, colorectal, prostate, and lung cancers who were treated with the therapy had longer overall and progression-free survival than patients who received standard-of-care palliative radiation therapy.

Stereotactic ablative radiotherapy (SABR), or stereotactic body radiation therapy, a focused, high-dose, and high-precision form of radiation therapy delivered in one or a few sessions, may improve survival of patients with metastatic cancer. In a phase II trial, patients with metastatic breast, colorectal, lung, and prostate cancers who were treated with SABR had longer overall survival (OS) and progression-free survival (PFS) than patients who received lower-dose standard-of-care palliative radiation therapy. Results of the trial were presented at the 2018 American Society for Radiation Oncology Annual Meeting in San Antonio, TX, October 21–24.

“In the past, patients with metastatic cancers have generally been considered to be incurable, and treatment would be aimed at prolonging life or slowing down the cancer, but not trying to cure the disease completely,” said David Palma, MD, of the London Health Sciences Centre in Ontario, Canada, who presented the findings. However, some data from single-arm and nonrandomized studies have suggested that patients with only a few small metastases might benefit from aggressive, localized treatment with SABR.

To investigate further, Palma and his colleagues launched the SABR-COMET trial, enrolling 99 patients with up to five metastases—mainly in the bones, liver, or lungs—from a variety of malignancies, most commonly breast, colorectal, lung, and prostate cancers. Patients were assigned 2:1 to receive either SABR targeted at the metastases or standard-of-care palliative radiation therapy.

Patients treated with SABR had a median OS of 41 months and a median PFS of 12 months, compared with 28 months and 6 months, respectively, in patients who received palliative therapy. Quality of life did not differ between the treatment arms, although 28.8% of patients treated with SABR had treatment-related side effects, compared with 9.1% of patients receiving palliative care. Additionally, three patients in the SABR arm died from side effects related to treatment, whereas there were no such deaths in the palliative care arm.

Palma acknowledged that the initial OS results, although promising, will require more time to mature—he and his team plan to follow patients for an additional 10 years. He added, however, that many drugs are approved based on PFS or other surrogate endpoints, “so we don't always need an OS benefit to treat.” The researchers will soon launch two phase III trials of SABR: one in patients with up to three metastases, and another in patients with four to 10 metastases.

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Paul Harari, MD, of the University of Wisconsin School of Medicine and Public Health and the Carbone Cancer Center in Madison, who was not involved in SABR-COMET, called it “an enormously powerful trial.”

“Can it change practice today? I believe it can, and I believe it will in some cases … it is up to oncologists to gauge and analyze this data,” he said. The trial “is opening the window to randomized, phase III controlled trials that will no doubt be carried out over the coming years to define very clearly and confirm this outcome, and better define the subsets and cohorts of patients for whom this is most likely to be effective.” –Catherine Caruso

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©2018 American Association for Cancer Research.
2018
American Association for Cancer Research.