Women age 65 and older who delay radiation treatment after breast cancer surgery run a greater risk of having their cancer recur, according to a study published online March 2 in the British Medical Journal.

Rinaa Punglia, MD, a radiation oncologist at Dana-Farber Cancer Institute and Brigham and Women’s Hospital in Boston, and her colleagues conducted the study to address the debate about the “appropriate interval between surgery and radiation treatment, or radiotherapy, and its impact on treatment outcomes.”

The researchers reviewed Medicare data records of 18,050 women with early-stage breast cancer to determine whether the timing of post-surgery radiotherapy affected outcomes. The women were treated between 1991 and 2002 with lumpectomy and radiation, but not chemotherapy. The median time from the last breast surgery to the start of radiotherapy was 34 days (with a range of one to 181 days), and the median follow-up time was 5.38 years.

According to the authors, 4 percent experienced local recurrences after radiotherapy, which increased to 5 percent when there was an interval of more than six weeks from the time of surgery until radiotherapy began. The authors found there was no particular threshold at which the risk of recurrence suddenly increased, but there is instead “a continuous relation between time to radiotherapy and local recurrence.”

“There isn’t a large difference between 43 days instead of 41,” said Punglia. “The day-to-day risk  increase is very small.”

What causes delays? One factor, the authors suggested, could be the increased use of breast-conserving surgery during the time period of the study. For example, in the Northeast U.S., the proportion of women whose radiation started more than six weeks after surgery increased from 23.8 percent in 1991-1992 to 42 percent in 2001-2002, while in the southern states—where the breast-conserving surgery rates are the lowest—there was little or no increase in the proportion or women receiving radiation after six weeks.

Longer times to radiotherapy during recent years and in regions of the U.S. known to have increased use of breast-conserving surgery suggested limitations in capacity of radiation delivery, according to the authors. “Indeed, our instrumental variable analysis showed an association between interval to radiotherapy and longer distances to treatment facility, providing further indirect evidence that lack of availability of radiotherapy is contributing to delays,” they wrote.

Punglia and colleagues concluded that there is no safe threshold when it comes to the interval between surgery and radiotherapy, and radiotherapy should start as soon as possible.

"The cost of increasing capacity to ensure uniformly short waiting times could be substantial,” they added. “These costs would need to be weighed against the small absolute benefit in local recurrence that might be the result of the investment. But given the known negative impact of local recurrence on overall survival and the large numbers of women treated with radiotherapy for breast cancer, it seems appropriate to consider whether this is a price we should be prepared to pay.”