ACCELERATED PATIAL BREAST IRRADIATION

ATLANTA — In a study of women with early breast cancer, outcomes with accelerated partial-breast irradiation (APBI) and traditional whole-breast irradiation (WBI) were comparable at 10 years.

The women received the radiotherapy after lumpectomy.

A matched-pair analysis revealed that were no significant differences between WBI and APBI in terms of local recurrence (4% vs 4%; P = .11), regional recurrence (1% vs 1%; P = .20), distant metastasis (3% vs 6%; P = .47), or overall survival (83% vs 75%; P = .34), said lead author Jessica Wobb, MD, from the Department of Radiation Oncology at the Beaumont Cancer institute in Royal Oak, Michigan.

In the study, 247 pairs of women were matched for age, tumor size, and estrogen-receptor (ER) status. The women were selected from a set of 3000 patients treated with either APBI or WBI at Beaumont from 1980 to 2012.

Dr. Wobb presented the data from the single-center series here at the American Society for Radiation Oncology 55th Annual Meeting.

Long-term cosmesis was good to excellent in 94% of WBI patients and 95% of APBI patients (P = .78). There was a trend toward slightly larger tumors in WBI patients than in APBI patients (13.0 vs 11.4 mm; P = .06).

At 10 years, there was no difference between WBI and APBI in terms of disease-free survival (93% vs 91%; P = .10) or contralateral breast failure (9% vs 3%; P = .06). In addition, 10-year cause-specific survival was similar (94% vs 93%; P = .72).

The series is one of only a handful of APBI datasets with at least 10 years of follow-up, Dr. Wobb said.

In this study, the APBI consisted of either interstitial catheter or balloon-based brachytherapy (MammoSite). "Accelerated partial-breast irradiation provides excellent local control in appropriately selected patients," Dr. Wobb concluded.

"Context is king," said study discussant Atif Khan, MD, from the Rutgers Cancer Institute of New Jersey in New Brunswick. Dr. Khan was referring to the fact that the population analyzed consisted of mostly low-risk patients, with a sprinkling of intermediate-risk patients. "APBI is appropriate in selected patients," he said, echoing Dr. Wobb.

A "risk-stratified approach" is key to choosing radiotherapy, he explained. In this setting, appropriate patients should have low-risk characteristics; they should be older than 50 years of age and have tumors that are small, unifocal, ER- or progesterone-receptor-positive, and have negative margins and negative nodes. Intermediate-risk patients should be those with breast cancers that are nonluminal A, ER-positive, and node-positive.

Dr. Khan posed a hypothetical question for clinicians: "Do all women undergoing breast-conserving therapy really need whole-breast radiotherapy?" Unfortunately, the matter of actually providing APBI to women is full of unresolved concrete technical matters, such as volume and the optimal treatment schedule, he said, explaining that the answer is not simple.

This study adds to the literature on APBI, which has provided a mixed bag of results, both favoring and disfavoring the newer partial-breast approach.

For instance, in May, 2012, 10-year results from the phase 3 Hungarian National Institute of Oncology trial showed that disease control and complications are equivalent in patients receiving APBI and WBI, but that APBI has the advantage of treatment brevity and better cosmetic outcome.

However, in the same month, American investigators retrospectively looked at Medicare claims data and found a 2-fold increased risk for subsequent mastectomy, as well as postoperative and radiation-related complications, with APBI, compared with WBI, at 5 years (JAMA. 2012;307:1827-1837).

The study authors and Dr. Khan have disclosed no relevant financial relationships.

American Society for Radiation Oncology (ASTRO) 55th Annual Meeting: Abstract 14. Presented September 23, 2013.