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Delaying radiation after breast cancer surgery increases recurrence risk in older women.

Older women who have had breast cancer surgery have a greater risk of the cancer returning if they delay their post-surgical radiation treatment, report Dana-Farber Cancer Institute scientists.

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 British Medical Journal published the findings online on March 2, 2010.

Rinaa Punglia, 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 northeastern United States, 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, who is also an HMS assistant professor of radiation oncology.

Although the study focused on older women, the findings have implications for younger women. “It’s possible,” Punglia said, “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.”

—Dana-Farber Cancer Institute press release

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