A three-week course of whole-breast irradiation after breast-conserving surgery is as effective and safe as the standard five-week program, according to research findings presented by Tim Whelan, BM, BCh, of McMaster University in Hamilton, Ontario, during the 30th annual San Antonio Breast Cancer Symposium in Texas.
After 10 years, so-called accelerated hypofractionated whole-breast irradiation demonstrated excellent local control of breast cancer, Whelan said. At the same time, results from a randomized controlled trial showed that the shorter program was not associated with excess long-term morbidity, he added.
The shorter regimen can help overcome those obstacles, Whelan said, but has not been widely adopted in the U.S. because of lingering concerns of long-term morbidity that were not dispelled by the five-year results of the study.
Whelan said that standard whole-breast irradiation involves 50 Gy of radiation given as 25 2-Gy fractions daily over five weeks. The shorter regimen gives 40 to 42.5 Gy in 15 or 16 2.7-Gy fractions over three weeks.
The researchers randomized 1,234 women with invasive breast cancer treated by lumpectomy with pathologically clear resection margins and negative axillary nodes to one of the two arms from April 1993 through September 1996. Median follow-up has reached 12 years, according to Whelan.
At five years of follow-up, the two regimens were virtually identical, he said, with a three percent local recurrence and similar cosmetic outcomes in each arm. At 10 years, local recurrence was higher—at 6.7 percent for the standard regimen and 6.2 percent for the shorter regimen—but still not significantly different between the arms, Whelan said.
Probability of survival was also not different, at 84.6 percent for the shorter regimen and 84.4 percent for the standard course. Cosmetic outcome was defined as a combination of skin and soft tissue toxicity, breast appearance, and noncancer deaths. For each aspect, Whelan said, "no difference was evident between the two arms."
The study was originally designed to demonstrate noninferiority, Whelan said, with a 5 percent difference in efficacy set as the cutoff for equivalence. In fact, the shorter regimen was slightly better than the standard regimen in efficacy and the 95 percent confidence interval was within the 5 percent pre-set difference, he said.
"There has been some gradual acceptance of the shorter schedule," commented Phillip Devlin, MD, of Brigham and Women's Hospital in Boston, who was not involved in the study. "In our clinic, we use this schema as a fallback when there are circumstances – including transportation circumstances—that make [the longer regimen] inconvenient."
Devlin said the regime is also more economic. "If it's 13 days shorter, it has to cost less,” he said.