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Conventional Whole-Breast vs. Partial-Breast Irradiation in Controlling Tumor Recurrence

By: Kayci Reyer
Posted: Friday, January 4, 2019

Based on the primary results of the NSABP B-39/RTOG 0413 (NRG Oncology) trial, presented at the 2018 San Antonio Breast Cancer Symposium (SABCS; Abstract GS4-04), partial breast irradiation (PBI) did not meet the criteria for equivalence to whole-breast irradiation (WBI) in controlling ipsilateral breast tumor recurrence postlumpectomy in women with early-stage breast cancer, where equivalency was based on a 50% increase in hazard ratio. However, Frank A. Vicini, MD, of St. Joseph’s Mercy Hospital, Pontiac, Michigan, and colleagues found that the 10-year rate of ipsilateral breast tumor recurrence differed by less than 1% between the two treatments.

“The risk of [a recurrence-free interval] event was statistically significantly higher for PBI compared to WBI, but the absolute difference in 10-year [recurrence-free interval] rate was also small (8.1% PBI vs. 6.6% WBI),” concluded researchers. “[Distant disease–free interval], [overall survival], and [disease-free survival] were not statistically different for PBI vs. WBI.”

The phase III study included 4,216 patients who had undergone lumpectomy and had 0 to 3 positive axillary nodes. Participants were randomly assigned to receive either PBI or WBI. PBI was administered twice daily with either brachytherapy or three-dimensional external-beam radiation in 10 fractions of 3.4 to 3.85 Gy. WBI was given once daily in 2 fractions of 50 Gy, with a sequential boost to the surgical site.

At a median follow-up of 10.2 years, 161 ipsilateral breast tumor recurrences occurred as first events (90 PBI vs. 71 WBI). A total of 95.2% of patients in the PBI group versus 95.9% in the WBI group had no ipsilateral breast tumor recurrence at follow-up. Toxicity was more common in the PBI cohort than in the WBI group, with the rate of grade 3 toxicity at 9.6% versus 7.1% and grade 4 and 5 at 0.5% versus 0.3%, respectively.

Disclosure: Study authors’ disclosure information may be found at SABCS.org.



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