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SAN ANTONIO -- Long-term data confirmed the safety of weekly hypofractionated radiation therapy (RT) in early breast cancer, results of the FAST trial found.

At 10 years, the rate of moderate and severe effects to normal tissue was 14.6% with a weekly 28.5 Gy regimen versus 9.1% with a daily 50 Gy RT regimen (5.5% difference, 95% CI -2.3 to 13.3), reported Murray Brunt, MD, of University Hospitals of North Midlands and Keele University in England.

And at 5 years, the rate of moderate/severe effects was similar as well, at 9.9% with the 28.5 Gy regimen versus 7.5% with a conventional RT schedule (2.4% difference, 95% CI -2.5 to 7.3).

"This was always a trial to see if five fractions was feasible, and I think we've shown that it is," Brunt said at a press briefing here at the American Society for Radiation Oncology (ASTRO) meeting, noting that FAST is part of a series of hypofractionation trials in the U.K. Next, FAST-Forward will test five fractions delivered over the course of 1 week.

"We're not suggesting that general fractionation should change," said Brunt, but he noted that daily treatment can be difficult for frail patients and those who travel long distances for treatment.

"For those frail patients, I actually think this is enough to discuss it with them," he said, who nearly all say, "'Can we come once a week?'" when offered the option.

"It is quite popular amongst the frail," Brunt said.

The phase III trial studied the effects to normal breast tissue with three RT schedules -- one conventional and two hypofractionated:

• 50 Gy in 25 daily 2 Gy fractions
• 30 Gy in five weekly 6 Gy fractions
• 28.5 Gy in five weekly 5.7 Gy fractions

But with the 30 Gy regimen, rates of late moderate/severe late effects were significantly higher compared with conventional RT at both 5 years (18.0% vs 7.5%, P<0.001) and 10 years (18.4% vs 9.1%, P=0.04).

In fact, patients treated with the 30 Gy course were two- to three-fold more likely to experience moderate or severe hardness (P=0.004) or shrinkage of the breast (P<0.001), spider veins (P=0.02), and build-up of fluid (P<0.001).

ASTRO moderator Catherine Park, MD, of the University of California San Francisco, agreed that for certain patients, the results in the 28.5 Gy group possibly provide another RT course to offer to the standard hypofractionation regimen.

"Sometimes people find it cumbersome to come in every day for 3 weeks, so if there are some patients for whom the logistics are difficult, then we could maybe offer this," she told 番茄社区app.

But Park cautioned that the data did not shed light on patients receiving chemotherapy -- FAST excluded those needing adjuvant or neoadjuvant chemotherapy and those requiring a RT boost in order to reduce any confounding factors.

"I can't see this being widely adopted immediately, but as we move forward it can be another approach that we can consider," she said.

Park explained that the field is slow to adopt any new fractionation schedule: "We've largely now shifted to hypofractionation after a long period of time where there have been thousands of patients treated with hypofractionation in different contexts, so that we understand it's quite safe and that the outcomes are going to be at least comparable if not better."

The researchers also looked at local breast cancer relapse, which was rare, with only 10 instances across the full patient population (1.3%, 95% CI 0.7-2.3), with three in each of the 50 Gy and 30 Gy arms, and four in the 28.5 Gy arm. And there were 96 deaths during the median 9.9 years follow-up, 33 in the 50 Gy group, and 30 in each of the two hypofractionated groups. The trial was not designed to test for differences in either.

From 2004 to 2007 the FAST (Faster Radiotherapy for Breast Cancer Patients) trial randomized 915 women from 18 U.K. centers to the three treatment arms. Patients were ages ≥50 and had early invasive breast cancer with no nodal involvement. RT effects on breast cancer tissue were assessed each year by a clinician for 10 years, with photo assessment at 2 and 5 years.

At 5 years (n=774), 63.0% of patients in the 50 Gy group had no side effects to their normal breast tissue, nor did 56.9% of the 30 Gy group and 61.3% of the 28.5 Gy group. At 10 years (n=392) these rates were 68.2%, 50.8%, and 55.4%, respectively.

Brunt said that fractionation sensitivity explained the observed differences: 30 Gy over five weekly 6 Gy fractions would be equivalent to a total radiation dose of 57.3 Gy over 25 daily 2 Gy fractions, while 28.5 Gy delivered over five weekly 5.75 Gy fractions would be would be equivalent to 52.5 Gy in 2 Gy fractions.

番茄社区app's Elizabeth Hlavinka contributed to this report.

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