In the middle of this year's Breast Cancer Awareness Month, women with breast cancer have heard some encouraging news about treatment. A hormonal therapy called letrozole, also known as Femara, may reduce the risk of breast cancer recurrence in postmenopausal women by 43 percent, according to a large international study that was stopped early to make the drug available to all of the participants.
The study was conducted with 5,187 women, and it was released early by The New England Journal of Medicine and will appear in their November 6 issue. Researchers evaluated the use of letrozole following approximately five years of tamoxifen, the standard treatment for women with breast cancer that grows in response to estrogen.
Because the growth of these breast cancers is fueled by estrogen, the aim of hormonal therapy is to cut cancer cells' access to estrogen, thereby preventing the return of the cancer. While tamoxifen blocks estrogen receptors on breast cancer cells, letrozole, a member of a class of drugs called aromatase inhibitors, suppresses estrogen. Tamoxifen should only be taken for five years, after which time it is no longer effective. But letrozole may be able to pick up where tamoxifen leaves off.
Aromatase inhibitors, however, are only effective in postmenopausal women, whose ovaries no longer produce estrogen. They are currently used in women whose breast cancers progressed despite taking tamoxifen.
Study chair Paul Gass, MD, PhD, director of breast cancer prevention at the Princess Margaret Hospital in Toronto points out that the many young women who become postmenopausal from chemotherapy are candidates for letrozole therapy.
Researchers found that after an average of 2.4 years of letrozole, 132 women taking the placebo, an inactive substance, developed a new breast cancer or a breast cancer recurrence, compared with 75 women who received letrozole. Researchers estimated that disease-free survival at four years would be 93 percent for women taking letrozole and 87 percent for the placebo group.
Women who received the letrozole therapy experienced low-grade hot flashes, arthritis and muscle pain more often than people not taking the therapy. Letrozole may also be associated with elevated cholesterol and osteoporosis, and ongoing studies are currently assessing those risks.
In addition to addressing safety issues, further research is needed to determine the optimal amount of time women should take the drug and if letrozole might be effective in women who have already stopped taking tamoxifen.
Treatment guidelines should available soon. For now, researchers say letrozole should be a consideration for women who have recently completed five years of tamoxifen. According to Dr. Gass, a variety of circumstances might make women good candidates. "Women who stopped taking tamoxifen a year ago, women who stopped taking it three years but are at high risk, or women who have serious side effects from tamoxifen should talk to their doctors about these results."
Coauthor Hyman Muss, MD, a professor of medicine at the University of Vermont and the Vermont Cancer Center, says women will have to weigh the risks and benefits. "These are exciting data, but five years after diagnosis, most women are going to do well," says Dr. Muss. "Letrozole is going to be more valuable to women with a somewhat higher risk for recurrence, such as those with more extensive lymph involvement or a larger tumor. It's got to be an individual decision."
