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SAN DIEGO -- Hypofractionated radiation appeared to be as safe and effective as conventionally fractionated radiation therapy for patients with breast cancer who underwent implant-based breast reconstruction following mastectomy, according to results from the FABREC randomized trial.

For the study's primary outcome of change in physical well-being score, patients in both groups reported similar scores 6 months after treatment (P=0.70), though women under the age of 45 reported higher scores with the use of hypofractionation versus conventional fractionation (P=0.049), reported Rinaa Punglia, MD, MPH, of Dana-Farber Cancer Institute in Boston.

"Our results support the use of hypofractionated radiation therapy for patients with implant-based reconstruction," Punglia said during a press briefing at the American Society for Radiation Oncology (ASTRO) annual meeting.

At a median follow-up of 40.4 months, there were no differences between the hypofractionated and conventionally fractionated groups in any of the oncologic outcomes, including distant recurrence (11 and 12, respectively), death (two in each arm), or local recurrence (one in each arm).

There were three cases of pneumonitis in the hypofractionated arm and one in the conventionally fractionated arm. Chest wall toxicity was reported in 20 and 19 patients, respectively.

Punglia also noted that treatment breaks -- which are associated with worse outcomes in breast cancer -- occurred at a significantly lower rate, and for shorter periods of time, in the hypofractionation arm (2.7% of patients for an average of 2.8 days) compared with patients in the conventional arm (7.7% of patients for an average of 3.3 days).

Younger women randomized to hypofractionation were less bothered by side effects than their peers treated with conventional fractionation (P=0.045).

In addition, patients in the hypofractionation arm took fewer hours of unpaid time from work for treatment: a mean of 73.7 hours versus 125.8 hours in the conventional arm (P=0.046).

Lori Pierce, MD, of the University of Michigan in Ann Arbor, called the study a "game changer."

"Tumor control was the same, there was no difference in side effects, and no difference in physical well-being," she pointed out. "And I cannot stress this point enough -- with hypofractionation, it is more convenient to patients."

Pierce said that since hypofractionation has been shown in randomized trials to be comparable to conventional fractionation regarding tumor control, survival, and toxicity, radiation oncologists routinely use it for patients who have had lumpectomy followed by breast radiotherapy.

However, she noted that about 40% of breast cancer patients undergo mastectomy, two-thirds of whom have implant based-reconstruction, and about one-third of whom need to have radiation after mastectomy.

"So, we are talking about a lot of patients here," she said. "We have been offering hypofractionation to those who have breast conservation and have not been offering it to those patients who have mastectomy and implant-based reconstruction. That's why I say FABREC is a game changer. It will potentially impact thousands of women who have had mastectomy and implant-based reconstruction."

The included 400 patients (median age 47 years) with stage 0 to III breast cancer treated with mastectomy and immediate implant-based reconstruction. Most (84.2%) had hormone receptor-positive disease, about two-thirds had received neoadjuvant chemotherapy, and 21.5% had received preoperative endocrine therapy.

Patients from 16 institutions were enrolled in the trial from March 2018 through November 2021 and randomized to receive hypofractionated radiation in 16 fractions of 266 cGy Monday through Friday for 3 weeks or conventionally fractionated radiation in 25 fractions of 200 cGy Monday through Friday for 5 weeks. Median time to the start of radiation therapy was 2.6 months.

Punglia acknowledged several limitations to the study, including the fact that study accrual partially took place during the COVID-19 pandemic, which may have changed practice patterns.

"And while breast-conserving surgery patients had improved quality of life at 6 months with hypofractionation, the patients in our cohort had much more treatment in terms of surgery and systemic therapy, which could have diluted the impact of shorter radiation," she added. "It's possible if an earlier timepoint had been assessed, a larger improvement in quality of life with hypofractionation would have been detected."

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