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CHICAGO -- More evidence supports the use of accelerated radiation therapy techniques as safe alternatives to standard options following breast-conserving surgery, according to researchers.

In the TRIUMPH-T trial, three-fraction accelerated partial breast irradiation (APBI) offered effective disease control with low toxicity compared with standard APBI, Catheryn Yashar, MD, of the University of California San Diego, reported.

Results from the MC1635 trial showed that extreme hypofractionated radiation therapy for localized breast cancer is as well tolerated and safe as moderate hypofractionation, said Cameron Thorpe, MD, of the Mayo Clinic in Phoenix.

Both studies were presented at the annual meeting of the American Society for Radiation Oncology (ASTRO).

TRIUMPH-T

The hypothesis behind the phase II TRIUMPH-T trial was that a shorter course of brachytherapy (22.5 Gy over 3 days; 7.5 Gy fractions) would be a promising alternative to standard 5-day/10-fraction APBI in eligible patients following breast-conserving surgery.

In all, 175 patients ages 45 years or older were enrolled. Median follow-up was 3.63 years at the time of analysis. Eligibility requirements included hormone-receptor positive unicentric invasive or in situ tumors ≤3 cm, with negative margins and no metastases to axillary nodes.

The researchers found:

• Excellent or good cosmesis in 95% of patients
• Grade 1/2 fibrosis at the treatment site in 32%
• Grade 3 fibrosis in 1.7%
• No grade 4 toxicities
• One rib fracture

Other late toxicities included hyperpigmentation (grade 1; 7.4%), telangiectasias (grade 1; 2%), symptomatic seromas (1.7%), abscessed cavities (1.7%), and symptomatic fat necrosis (1.1%).

There were two ipsilateral local recurrences (1.1%), two nodal recurrences (1.1%), no distant recurrences, one contralateral breast cancer, and two second lung malignancies.

"Ultra-short breast brachytherapy is feasible and has low toxicity, with good local control, and with the way we have calculated the dose, we expect the control rate to stay good," Yashar concluded. "We believe this is a good alternative to 5-day/10-fraction APBI in eligible patients."

"This is more data to continue to support our comfort with a once-daily treatment for APBI," said ASTRO discussant Elizabeth Nichols, MD, of the University of Maryland in Baltimore. "The optimal total dose and fractions still need to be determined."

MC1635

This phase III trial randomized 107 patients with localized breast cancer (T1-T3, N0-N1, M0) managed with breast-conserving surgery 1:1 to whole-breast radiotherapy with moderate (40 Gy over 15 fractions) or extreme hypofractionation (25 Gy over five fractions).

More than half (55%) had invasive ductal carcinoma, while 20% had invasive lobular carcinoma, 16% had ductal carcinoma in situ, and 9-10% had mixed or other subtypes. For tumor grade, 31% had grade 1 tumors, 41% had grade 2, and 28% had grade 3 tumors.

Over a median follow-up of 20 months:

• Grade 2 toxicities were seen in 7.4% of patients in the moderate hypofractionation arm and 7.5% of those in the extreme arm -- consisting mostly of radiation dermatitis in six patients, and fibrosis and lymphedema in one patient each
• Deterioration in cosmesis 3 months or more after radiotherapy was seen in 1.6% and 1.7% of the two arms, respectively
• The average Harvard cosmesis score was similar between arms at all timepoints, and quality of life (QoL) scores were similar as well
• No cancer deaths or recurrences were seen in either arm

Thorpe said that patient-reported mild-to-worse skins burns were more commonly reported in the moderate hypofractionation arm compared with the extreme hypofractionation arm (58.7% vs 27.9%).

"MC1635 suggests that extreme hypofractionation with 25 Gy in five fractions for early breast cancer is well tolerated compared to moderate hypofractionation, with similar [QoL] and cosmesis between arms," he concluded.

"This study really confirms -- just like the study -- a great toxicity profile between the moderate hypofractionation arm and the extreme hypofractionation arm, and similar QoL and toxicities," said Nichols.

"We continue to have ongoing questions," she added. "Is it safe to treat the nodes? Is it going to be better or worse with certain subtypes of breast cancer? Will it be OK to give with/during other therapies? What are the potential long-term toxicities regarding cardiac and pulmonary outcomes? And will there be an effect on the reconstructed breast?"