August 26, 2009

Tamoxifen May Increase 2nd Breast Cancer Risk

Treating breast cancer using hormonal therapy with drugs like tamoxifen has been shown to reduce the risk of dying from the disease, but a new study suggests it is not without risk.
While long-term tamoxifen use among breast cancer survivors decreases their risk of developing the more common, less aggressive type of second breast cancer, its use is also associated with a more than four-fold increase of a more aggressive, difficult-to-treat type of cancer in the breast opposite to that with the initial tumor.

Christopher Li, M.D., Ph.D., and colleagues at Fred Hutchinson Cancer Research Center in Seattle compared breast-cancer patients who received the estrogen-blocking drug tamoxifen to those who did not. They found that the drug was associated with a 60 percent reduction in estrogen receptor-positive, or ER positive, second breast cancer "“ the more common type, which is responsive to estrogen-blocking therapy.

Tamoxifen use also appeared to increase the risk of ER negative second cancer by 440 percent. "This is of concern, given the poorer prognosis of ER-negative tumors, which are also more difficult to treat," Li, an associate member of the Hutchinson Center's Public Health Sciences Division, is quoted as saying.
These findings confirmed earlier research by Li and colleagues. "The earlier study had a number of limitations. For example, we did not have information on the duration of tamoxifen therapy the women received," Li said. "The current study is larger, is based on much more detailed data, and is the first study specifically designed to determine whether tamoxifen use among breast cancer survivors influences their risk of different types of second breast cancers."
This new study assessed history of tamoxifen use among 1,103 breast cancer survivors from the Seattle-Puget Sound region who were initially diagnosed with ER-positive breast cancer between the ages of 40 and 79. Of these, 369 developed a second breast cancer. Nearly all of the women in the study who took hormonal therapy used tamoxifen specifically.

While the study confirmed a strong association between long-term tamoxifen therapy and an increased risk of ER-negative second cancer, it does not suggest that breast cancer survivors should stop taking hormone therapy to prevent a second cancer, Li said.
"It is clear that estrogen-blocking drugs like tamoxifen have important clinical benefits and have led to major improvements in breast cancer survival rates. However, these therapies have risks, and an increased risk of ER-negative second cancer may be one of them," said Li. "Still, the benefits of this therapy are well established and doctors should continue to recommend hormonal therapy for breast cancer patients who can benefit from it."

SOURCE: Cancer Research, August 25, 2009