Use of radiation therapy dramatically reduces recurrence rates.

Toronto (Aug. 31, 2004) - A new study by Canadian researchers proves a woman's chance of breast cancerreturning after surgery is significantly reduced by following up with radiation therapy and tamoxifen. The study, published in tomorrow's edition of the prestigious international journal New England Journal of Medicine, was attempting to determine if women with low-risk breast cancer could avoid radiation therapy after surgery.

The study, lead by Dr. Anthony Fyles, a Radiation Oncologist at Princess Margaret Hospital, Senior Scientist with the Ontario Cancer Institute, and Professor with the University of Toronto, compared 769 women, 50 years or older, whose early-stage breast cancer had been treated by lumpectomy. Half of the women received further treatment with tamoxifen and radiation, while the other half received tamoxifen alone. Those with the combined tamoxifen and radiation treatment were seven per cent less likely to see their cancer recur in the breast within five years after initial treatment.

At five years, only 0.6 per cent of women receiving the tamoxifen and radiation treatment had a breast relapse, compared with 7.7 per cent for those women taking tamoxifen alone. The researchers had not expected to see such a dramatic difference between the two groups, nor that the combined therapy would reduce the risk of breast cancer recurrence to nearly zero.

"These findings are important for women who fear the possible return of their breast cancer," said Dr. Fyles, the study's lead author. "Although the overall risk of the cancer returning after surgery is small, there remains a significant benefit to post surgery radiation treatment."

Those women who benefited the least from radiation treatment were patients aged 60 or older, with very small tumors, whose rate of relapse without radiation was 1.2 per cent. Another study published in the same issue of the journal examined a smaller subgroup of women (aged 70 or older, with small tumors that were positive for estrogen receptors) and found only a three per cent difference between those treated by lumpectomy and tamoxifen alone as compared with women who also received radiation treatment.

"Based on our findings, women should continue to thoroughly discuss with their doctors the risks andbenefits of the treatment and make an appropriate decision based on their individual circumstances and tolerance for risks of relapse and toxicity," said Dr. Fyles.

The study was supported by the Ontario Ministry of Health and Long-Term Care, the Princess Margaret Hospital Foundation, and the Canadian Breast Cancer Foundation (British Columbia and Yukon chapter). The study involved researchers from Princess Margaret Hospital, Toronto Sunnybrook Cancer Centre (Sunnybrook and Women's College Health Sciences Centre), University of Toronto, and the British Columbia Cancer Agency.

About Princess Margaret Hospital

Princess Margaret Hospital and its research arm, Ontario Cancer Institute, have achieved an international reputation as global leaders in the fight against cancer. Princess Margaret Hospital is a member of the University Health Network, which also includes Toronto General Hospital and Toronto Western Hospital. All three are teaching hospitals affiliated with the University of Toronto.

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