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Women who took letrozole (Femara®) were 43 percent less likely to experience a recurrence compared to women who took a placebo. The study, begun in 1998, was stopped ahead of schedule in 2003 when the positive effects became clear, so that the women taking a placebo could be offered the drug.
The Canadian-led study of more than 5,000 women was made possible by a public-private partnership between the Canadian Cancer Society, NCI, and Novartis Pharmaceuticals, the company that makes Femara.
These results have major implications. More than half of breast cancer survivors are postmenopausal and take a five-year course of tamoxifen after their initial treatment. The drug tamoxifen deprives breast cancer cells of estrogen and
can reduce breast cancer recurrence by 47 percent. Unfortunately, resistance to tamoxifen develops over time, limiting the duration of tamoxifen's effectiveness to 5 years. Up until now, no treatment has been available for women after they complete the five-year course of tamoxifen.
"More than half of women who develop recurrent breast cancer do so more than five years after their original diagnosis," says Paul Goss, M.D., Ph.D., of Princess Margaret Hospital in Toronto. "For years, we have thought that we had reached the limit of what we could do to reduce the risk of recurrence with five years of tamoxifen. Our study ushers in a new era of hope by cutting these ongoing recurrences and deaths from breast cancer after tamoxifen by almost one half." Goss, a leading expert in novel hormone therapies for the treatment and prevention of breast cancer, conceived of and chaired the international trial with letrozole.
While both tamoxifen and letrozole block estrogen's growth-promoting action on tumor cells dependent on this hormone, they do so in different ways. Tamoxifen blocks estrogen from binding to cancer cells, whereas letrozole actually reduces the body's production of estrogen.
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