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Toronto (Oct. 19, 2003) - A major international clinical trial conceived and chaired by Dr. Paul Goss, a medical oncologist at Princess Margaret Hospital, has shown that the drug letrozole given after tamoxifen reduces by 44 per cent the chance of breast cancer returning in post-menopausal women.
The results of the research are so positive that an independent safety monitoring committee recommended that the clinical trial end early so any participants receiving a placebo can be offered the chance to receive letrozole.
The study, published today in a special advance on-line edition of the New England Journal of Medicine, involved 5,187 women from nine countries including Canada, the United States, Europe and the United Kingdom. It compared letrozole to placebo for keeping cancer at bay in post-menopausal breast cancer survivors who had completed five years of treatment with the drug tamoxifen.
The results showed a startling 44 per cent reduction in the chances of the breast cancer returning for those women taking letrozole compared to those taking a placebo. There was a reduction in internal metastases, local recurrences and new tumors in the opposite breast. Breast cancer deaths were cut in half.
About two thirds of all post-menopausal breast cancer survivors take tamoxifen to ensure the cancer does not return. Yet studies show that after about five years tamoxifen loses its effectiveness, leaving these women with no known effective therapies thereafter.
"For the first time we have proof of an effective long-term treatment option for these women who are at risk of their breast cancer recurring," said Dr. Goss, a leading expert in novel hormone therapies for the treatment and prevention of breast cancer. "Our study ushers in an era of new hope by cutting these ongoing recurrences and deaths from breast cancer after tamoxifen by half."
Participants in the clinical trial took either letrozole in pill form or a placebo on a daily basis for between 2.5 and five years. Letrozole is one of the new classes of drugs called aromatase inhibitors, which works by suppressing estrogen levels - a major factor in the growth of many breast cancers. Side effects reported included those similar to women undergoing menopause, and were considered mild. Mild thinning of the bones is a possible long term side effect and Dr Goss cautions that women taking this drug should be advised to take calcium and Vitamin D according to standard guidelines for postmenopausal women and should be closely monitored with bone mineral density tests. "Further analysis of the data from our trial will help to clarify the extent of bone loss," says Dr Goss, who is also a professor at the University of Toronto.
The study was supported by funding from the Canadian Cancer Society and Novartis Pharmaceuticals, which manufactures letrozole under the brand name Femara. The trial was coordinated with the National Cancer Institute of Canada Clinical Trial Group (NCIC-CTG) at Queen's University and in partnership with the U.S. National Cancer Institute.
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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