Data from the NRG (NSABP B-39/RTOG 0413) trial indicated that ipsilateral breast tumor recurrence (IBTR) rates 10 years after treatment could not reject the hypothesis that accelerated partial breast irradiation (PBI) after lumpectomy was inferior to whole breast irradiation (WBI), according to a presentation at the 2018 San Antonio Breast Cancer Symposium, held Dec.

Moreover, the 10-year estimates for relapse-free interval (RFI) disclosed a statistically significant inferiority for PBI compared to WBI. Because the differences relative to both IBTR and RFI were small, PBI may be an acceptable alternative to WBI for a proportion of women who undergo breast-conserving surgery.

"Because of advancements in screening and public awareness, the majority of breast cancer patients in the U.S. are diagnosed in early stages, and over 100,000 women each year face treatment decisions about breast-conserving therapy," said Frank Vicini, MD, principal investigator at the MHP Radiation Oncology Institute/21st Century Oncology in Pontiac, Michigan.

Radiation treatment

"It is important that breast cancer patients and the health care system have modern information about breast-conservation treatment and options that can improve access to care, combat overtreatment, reduce the burden of treatment and health care costs, and improve quality of life," said Vicini.

WBI following lumpectomy has comparable ipsilateral recurrence rates compared to mastectomy, Vicini explained. Accelerated PBI treats the tumor bed area instead of the entire breast and reduces radiation treatment time from 3-6 weeks to 5-8 days, he noted.

"The main purpose of our study was to determine if accelerated PBI is equivalent to WBI in controlling for ipsilateral breast cancer recurrence in women who desire breast-conservation surgery," he said.

Vicini, Julia White, MD, co-principal investigator at The Ohio State University, and colleagues randomized breast cancer patients who had recently received a lumpectomy with 0-3 positive axillary nodes to treatment with WBI or PBI.

Of these breast cancer patients, 25% had ductal carcinoma in situ (DCIS), 65% had stage I breast cancer, and 10% had stage II breast cancer. Eighty-one percent of patients had hormone receptor-positive cancer, and 61% of patients were postmenopausal.

Of the 4,216 breast cancer patients, 2,109 received WBI and 2,107 received PBI. Treatment with WBI was defined as daily treatment with 2 grays (Gy) of radiation totaling 50 Gy with a sequential boost to the surgical site; treatment with PBI was defined as twice daily treatment with 3.4-3.85 Gy totaling 10 treatments delivered via 3-D external beam radiation or brachytherapy.

The primary endpoint of the trial was evidence of IBTR. Secondary endpoints included RFI, distant disease-free interval (DDFI), and overall survival (OS). The median follow-up time was 10.2 years. Disease-free survival (DFS) was also analyzed.