Interim analysis data from a randomized Phase III trial reported at the American Society of Clinical Oncology's 47th Annual Meeting showed that, in women with node-positive or high-risk node-negative breast cancer, additional regional nodal irradiation (RNI), improves disease-free survival, reducing cancer recurrences both near the tumor site and in other parts of the body. In addition, overall mortality was reduced by 24 percent in the group receiving RNI, but this did not reach statistical significance.

"These results are potentially practice-changing. They will encourage physicians to offer all women with node-positive disease the option of receiving regional nodal irradiation," said Dr. Timothy J. Whelan, BM BCh, lead study investigator for the NCIC Clinical Trials Group and a professor of oncology and Division Head of Radiation Oncology at McMaster University and the Juravinski Cancer Centre, Hamilton, Ontario. "Adding regional nodal irradiation improved disease-free survival, lowered the risk of recurrences, and there was a positive trend toward improved overall survival, while not greatly increasing toxicities."

Women with node-positive breast cancer are treated with breast-conserving surgery plus axillary lymph node dissection, followed by whole breast irradiation (WBI). If a woman's cancer has high-risk features, such as a tumor larger than 5 cm or more than three positive axillary nodes, she often receives regional nodal irradiation, or RNI. However, for women with one to three positive nodes, the benefit of adding RNI has been unclear.

The study enrolled 1,832 women, most of whom (85 percent) had one to three positive lymph nodes, and a smaller proportion of women (10 percent) who had high-risk, node-negative breast cancer. All women had been treated with breast-conserving surgery and adjuvant chemotherapy or endocrine therapy. The participants were randomized to receive either WBI alone or WBI plus RNI.

A protocol specified interim analysis of the data conducted in March 2011 found that after a median follow up of 62 months, there were statistically significant benefits for the group receiving the added RNI therapy. These included a greater than 30 percent improvement in disease free survival (from 84 percent for those who received WBI to 89.7 percent for those who also got RNI at 5 years), as a result of a 41 percent lower rate of recurrences near the tumor site (from 5.5 percent to 3.2 percent at 5 years), and a 36 percent lower rate of cancer recurrences in other parts of the body (from 13 percent to 7.6 percent at 5 years).

The patients who received the added RNI had a low but statistically significant increased risk of grade 2 or greater pneumonitis and lymphedema.