A large analysis of women with breast cancer who underwent accelerated partial breast irradiation using brachytherapy (APBIb) revealed that two-thirds would have been deemed cautionary or unsuitable for the procedure based on guidelines later set forth by the American Society for Radiation Oncology (ASTRO).

Surveillance, Epidemiology, and End Results (SEER) data for 138,815 women who received diagnoses of nonmetastatic breast cancer between 2000 and 2007 showed that after breast-conserving surgery, 2.6% (3,576) received APBIb; the remainder underwent whole-breast irradiation (WBI). Although results from prospective randomized phase III trials comparing the two techniques are not expected for several years, APBIb use increased from 0.4% in 2000 to 6.6% in 2007, demonstrating the rapid adoption of this approach in the United States, particularly in white women with lower-grade tumors who lived in cities.

However, only 32% of the APBIb patients would have been considered suitable for this treatment under ASTRO guidelines published in 2009, after the study period. But as Jona Hattangadi, MD, of the Department of Radiation Oncology at Brigham and Women’s Hospital and Harvard Medical School, both in Boston, Massachusetts, pointed out in Journal of the National Cancer Institute (2012;104:29-41), the data used to derive these guidelines were available to providers making ABPIb treatment decisions.

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An additional 29.6% of women undergoing APBIb would have been labeled “cautionary,” and 36.2% would have been classified as unsuitable.

Reassuringly, the steepest increase in APBIb use was seen among suitable patients (from 0.7% in 2000 to 11% in 2007). Older age was an important predictor of ABPIb use in all patients, with women 60 years and older being twice as likely to receive APBIb than were those younger than 50 years. This is consistent with the ASTRO guidelines, which suggest that patients 60 years and older may be suitable for APBIb off-protocol.

According to ASTRO, women with pure ductal carcinoma in situ (DCIS) are cautionary (for tumors up to 3 cm) or unsuitable (for tumors larger than 3 cm) for APBIb due to a lack of long-term data when the guidelines were written, but the current study indicates that APBIb utilization is rapidly increasing for all DCIS patients.

Estrogen receptor (ER)-positive tumors are considered suitable for APBIb whereas ER-negative tumors are considered cautionary. Among the “unsuitable” women analyzed, those with ER-negative tumors were 25% less likely to receive APBIb than were ER-positive patients.