The study, which involved more than 18,000 women age 65 and older who had breast cancer, found that those who started radiation treatment more than six weeks after breast-conserving surgery were more likely to have a local recurrence than those whose radiation treatment started within six weeks of surgery. The findings are being published online by the British Medical Journal.

Rinaa Punglia, MD, MPH, a radiation oncologist at Dana-Farber and Brigham and Women's Hospital and the study's lead author, said she and her colleagues conducted the research to address scientifically the debate about the "appropriate interval between surgery and radiation treatment, or radiotherapy, and its impact on treatment outcomes."

Post-surgical radiotherapy is designed to destroy remaining cancer cells following the removal of a localized breast tumor. Punglia said four to six weeks after surgery is widely viewed as a safe interval for beginning radiotherapy, which typically is administered five days a week for six weeks.

The researchers reviewed Medicare database records of 18,050 women with early stage breast cancer to assess whether the timing of when radiotherapy started following surgery affected outcomes. These women were treated between 1991 and 2002 with lumpectomy and radiation, but not chemotherapy. Thirty percent of women began radiotherapy six or more weeks after surgery.

For the overall group, slightly more than 4 percent of the women experienced a local recurrence. The risk increased to about 5 percent, approximately a 19 percent jump, when the surgery-radiotherapy interval was longer than six weeks. The researchers found that there was no "threshold" at which the risk suddenly rose -- it increased incrementally day by day. "There isn't a large difference between 43 days instead of 41," commented Punglia. "The day-to-day risk increase is very small."

The rise in breast-conserving surgery in the past two decades has fueled greater demand for radiotherapy, and might be one cause of longer waiting times. The study revealed more delays in areas such as the Northeast, where the procedure is more common, and fewer delays in the southern states, where breast-conserving surgery is less common.

Waiting times were also longer in cases involving African-American and low-income women, but the study did not pinpoint the exact source of the delay. "It could be factors such as access to care, the patients' ability to navigate the healthcare system, or physician referrals," said Punglia.

Although the study focused on older women, the findings have implications for younger women.

"It's possible that the increased risk we identified in older women could be magnified in younger women, whose tumors are biologically different and tend to be more aggressive," said Punglia, who is also an assistant professor of radiation oncology at Harvard Medical School.

The study's other authors are Bridget Neville, MPH, and Jane Weeks, MD, MSc, of Dana-Farber; Craig Earle, MD, formerly of Dana-Farber and now of the Ontario Institute for Cancer Research, Toronto; and Akiko Saito, MD, PhD, formerly of Dana-Farber and now of Nagoya Medical Center, Japan.

The research was supported by grants from the National Institutes of Health and the American Society of Clinical Oncology.

Note: If no author is given, the source is cited instead.

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