Data from a number of clinical trials presented at the ASTRO 2020 Annual Meeting continued to fortify earlier findings that demonstrated the benefits of stereotactic ablative radiotherapy (SABR) in treating patients with different types of cancer, including cancers that have metastasized.
Long-term follow-up findings from the SABR-COMET Randomized Trial testing outcomes in breast, lung, colorectal, and prostate cancers showed the magnitude of benefit eclipsed the original report and proved to be durable beyond 5 years.
Median overall survival (OS) for SABR patients was longer than for patients who underwent standard treatment at 50 months versus 28 months, as were 5-year OS rates at 17.7 percent and 42.3 percent. After 51 months, median progression-free survival was 5.4 and 11.6 months, respectively, while the corresponding 5-year progression-free survival rates were 0 percent and 17.3 percent.
"Significant rates of salvage SABR might indicate that undetected micrometastatic disease at presentation could be salvaged with SABR at progression," noted lead investigator David A. Palma, MD, PhD, Associate Professor in Medicine at Western University, London, Ontario. "With longer follow-up, the magnitude of benefit of SABR was more than in the original report and durable beyond 5 years."
He and his colleagues also reported that quality-of-life rankings between the two cohorts were similar. Reported grade 2-5 adverse events with SABR were 9 percent versus 29 percent, with no change over time; one and nine patients in Arms 1 and 2 received salvage SABR, respectively.
Preliminary results of SABR-COMET were presented at the ASTRO 2018 Annual Meeting, and published the following year in Lancet.
This year, the researchers reported that long-term control of lesions was better in the second arm at 63 percent versus 46 percent, and follow-up systemic therapy rates were similar between groups. One and nine patients in both cohorts received salvage SABR, respectively.
Findings From Down Under
Another study, by investigators at 134 centers in Australia and New Zealand, showed the benefits of SABR in treating cancer that has begun to spread throughout the body.
The research, conducted across 13 medical centers in Australia and New Zealand, strengthens the case for radiation therapy as a treatment for cancer that has begun to spread throughout the body.
At a news briefing Shankar Siva, PhD, Associate Professor of Radiation Oncology and Head of the SBRT program at the Peter MacCallum Cancer Centre, in Melbourne, Australia, presented positive findings from the SAFRON Phase II trial, a randomized trial in patients with up to three lung metastases (Abstract 5).
They found that patients treated with SABR in one or four sessions fared as well as their counterparts given standard drug therapy.
"I think the future of radiation oncology could be these ultra-short treatments," noted Siva. "Our results indicate that SBRT can be a safe and effective treatment for patients whose cancer has spread to their lungs, even when it's delivered in a single session."
He noted that almost half of all cancers spread to the lungs, the second most common site for metastases to occur.
"For patients with a limited number of metastases, recent studies have shown that there can be long-term survivors with the use of SBRT," he stated. "These studies tend to be smaller institutional series with a wide variety of SBRT regimens, so we designed our trial to test the safety and effectiveness of SBRT in a more robust fashion."
In the study, 90 patients were randomized into two treatment arms: half received a single fraction of 28Gy and the other half received a biologically equivalent regimen of four fractions of 12Gy each. Each patient had up to three lung metastases from primary tumors in other sites, most commonly colorectal cancer (47%). A total of 37 patients in each treatment group were eligible for safety analyses at 1 year after treatment.
In patients who received a single treatment, two patients had grade 3 side effects, including fatigue, loss of breath, and chest pain; however, no patients experienced grade 4 or 5 side effects. In patients who received four SBRT treatments, one died from pneumonitis within 3 months of treatment. There were no grade 3 or 4 events.
Siva explained that the events on the single-fraction arm lasted less than 3 months and his team found undiagnosed interstitial lung disease in the patient who died on the four-fraction arm. The researchers also found 1-year survival rates in both groups were nearly identical.
Local control rates were 93 percent for patients who received a single SBRT treatment, compared to 95 percent for those who received four treatments; overall survival rates were 95 percent and 93 percent; and disease-free survival rates were 59 percent and 60 percent.
Siva said the team will continue to analyze these secondary endpoints up to 3 years after treatment, as well as quality of life and cost effectiveness. Shorter treatment courses are especially welcome during the current pandemic, he noted.
"In a pandemic, the idea of a single, non-invasive outpatient treatment that doesn't require anesthesia is appealing in the sense of reducing patient time and transmission risk in the clinic," he said.
SBRT is typically spread out over up to five treatment sessions. "When we compress a multi-treatment course into a single treatment, there is a potential risk of higher toxicity. Based on our own anecdotal experience, we are quite comfortable using the single treatment approach. But globally, it's used less often," explained Siva.
There also are concerns that a single treatment might not have the same kind of effectiveness as multiple treatments. Thankfully, in this study, at least a year out, researchers saw similar efficacy, where 93-95 percent of the tumors were controlled in both arms.
"I think the future of radiation oncology could be these ultra-short treatments," said Siva. "Our results indicate that SBRT can be a safe and effective treatment for patients whose cancer has spread to their lungs, even when it's delivered in a single session.
"Our final analysis will show if this holds for the long-term, but these early results indicate that single fraction radiation could be carried out equally effectively across multiple institutions."
Kurt Samson is a contributing writer.