Patients whose cancer returns at multiple sites after treatment — called oligometastatic cancer — are generally thought incurable, but a recent Phase 2 trial found that a highly precise form of radiation can significantly extend these patients’ lives if the spread shows small tumors, without diminishing life quality.
The approach was tested in patients with up to five metastatic sites, and doubled the time a patient lived without disease progression.
The findings will be presented next week at the American Society for Radiation Oncology (ASTRO) 2018 Annual Meeting. David Palma, MD, PhD, a researcher at Lawson Health Research Institute – the research institute of London Health Sciences Centre (LHSC) and lead institution of the multi-center study – will be presenting the research.
“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,” Palma said in a press release. “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.”
Stereotactic ablative body radiotherapy (SABR), also known as stereotactic body radiation therapy (SBRT), is a kind of precision radiation therapy that uses small, thin beams of radiation directed into the tumor from different angles. The treatment delivers high radiation doses, requiring only one or a few sessions, and because it’s precise, healthy tissues nearby are spared.
Given the significant reduction in side effects compared to older radiation therapy approaches, researchers hypothesized the SABR could be used to ablate multiple metastatic lesions in cancer patients.
They designed a Phase 2 trial, called SABR-COMET (NCT01446744), that compared SABR with standard radiation approaches in patients whose cancer had been controlled but returned in up to five distinct locations.
The study included 99 patients from Canada, Scotland, the Netherlands, and Australia, whose most common cancers included breast (18%), lung (18%), colon or rectum (18%), and prostate tumors (16%); all had a life expectancy of more than six months. The majority of patients (93%) had their cancer spread to one to three new sites.
Patients in the trial (median age 68, 59% men) were randomly assigned SABR – given every other day for one to three weeks, depending on the disease site – or palliative radiation therapy. For each patient receiving standard of care, two were given SABR. Patients in both groups were allowed to receive concomitant chemotherapy, at the discretion of the medical oncologist.
Researchers found that SABR significantly extended patients’ lives by more than one year. While those receiving this approach lived for a median of three years and five months, patients on palliative radiation therapy lived two years and four months.
Stereotactic radiation also doubled the time patients lived without their disease progressing from six to 12 months. Interestingly, the survival benefits didn’t appear to take a toll on quality of life, as patients reported similar scores for physical, social, functional, and emotional scales.
Five years after treatment, nearly half (46%) of patients who received SABR were still alive, which was nearly double the 24% seen in patients receiving palliative radiation.
“We were surprised and quite pleased. We didn’t expect the survival benefit to be quite so long for patients with metastatic disease,” said Palma, also a clinician-scientist at the Ontario Institute for Cancer Research, which provided funding for this study.
Severe side effects were more common among those receiving SABR (30%) than in patients given standard of care (9%). The most common were fatigue, difficulty breathing, and pain. Three patients died due to SABR-related adverse events.
“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[s] to outweigh these risks,” said Palma.
During the trial, some patients developed more lesions that were also successfully treated. Researchers are now designing a follow-up trial, called SABR-COMET-10, that will test the approach in patients with as much as 10 metastatic lesions.
“We don’t know the upward limit of how many tumors can be treated with SABR,” Palma 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.”
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