Cancer Fighter

By Alice Park

For postmenopausal women who have been treated for breast cancer, five is a magic number. The standard therapy for tackling the majority of their tumors is surgery to remove the lumps, then the drug tamoxifen for five years to prevent cancer from recurring. After five years, the body becomes resistant to tamoxifen's effects. At that point, women stop taking it, cross their fingers and hope for the best. "There wasn't really anything available for them," explains Dr. Andrew von Eschenbach, director of the National Cancer Institute. "Yet we knew that many women risk recurrences even beyond five years."

Last week researchers involved in an international study finally gave these women a way to keep fighting their cancer beyond five years. In a study that the New England Journal of Medicine published online, the doctors report that a currently available drug, letrozole (marketed by Novartis as Femara), could pick up where tamoxifen leaves off. In a trial involving more than 5,100 women, those taking letrozole after five years on tamoxifen experienced 43% fewer cancer recurrences than those assigned to the placebo group. The benefit was so great that doctors decided to cut the trial short to give the placebo group the option of switching to letrozole.

Each year about 212,000 women in the U.S. are found to have breast cancer; half of them are postmenopausal and have tumors studded with receptors for estrogen or progesterone. These growths are perfect targets for tamoxifen and letrozole, which block estrogen's tumor-enhancing effects, albeit through two different mechanisms. "Estrogen is like the fuel that runs a car engine," says Dr. James Ingle, who headed the U.S. portion of the trial at the Mayo Clinic. "If you remove the fuel, the engine quits running."

The shortened trial did leave some questions unanswered. No one can say how long women should remain on letrozole. And while bone thinning is a known side effect, other long-term effects are unclear. Still, for those who have graduated from tamoxifen, there is finally something better than just hoping for good luck.