Long-term Tamoxifen Use Increases Risk of Aggressive Breast Cancer
Tuesday, September 29, 2009 by: S. L. Baker, features writer

Women with estrogen receptor-positive (ER positive) breast cancer are commonly prescribed the drug Tamoxifen because it blocks the effects of estrogen in breast tissue. In fact, long-term Tamoxifen use among ER positive breast cancer survivors has become a standard therapy. According to the National Cancer Institute (NCI), side effects of the drug range from hot flashes, vaginal dryness, joint pain and leg cramps to blood clots, cataracts, strokes and uterine cancer. Understandably, many women are willing to accept these risks because they are told Tamoxifen decreases their chance for a recurrence of breast cancer. However, a new study by Christopher Li, M.D., Ph.D., and colleagues at Fred Hutchinson Cancer Research Center just published online in the journal Cancer Research seems to reveal the belief that Tamoxifen protects against breast cancer is only partially correct. The drug may also cause certain breast cancers.

Yes, breast-cancer patients who receive long-term estrogen-blocker Tamoxifen therapy have a 60 percent reduction in their incidence of a second, ER positive breast cancer -- a common type of breast cancer which tends not to be aggressive and is responsive to estrogen-blocking therapy. But the new research shows Tamoxifen increases the risk of the women developing a second and far more dangerous type of breast cancer by a stunning 440 percent.

This type of ER negative cancer develops as a malignant tumor in the breast opposite, or contralateral, to the initial tumor. It is an aggressive, difficult-to-treat type of cancer with a poor prognosis. In other words, it is far more likely to spread and potentially kill.

The new findings by Dr. Li and his research team confirm earlier research published in 2001 by the same group of researchers which suggested a link between long-term Tamoxifen use and a heightened risk of ER-negative second cancers. "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 in a statement to the media. "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."

For the new study, the scientists investigated the history of Tamoxifen use among 1,103 breast cancer survivors from the Seattle-Puget Sound region. The women were initially diagnosed between the ages of 40 and 79 with ER positive breast cancer and 369 of them later developed a second breast cancer. Virtually all of the women in the study who took adjuvant hormonal therapy were placed on Tamoxifen to block estrogen.

Predictably, Dr. Li says the findings do not mean women should stop taking Tamoxifen therapy if their doctors say they need it. "However, these therapies have risks, and an increased risk of ER negative second cancer may be one of them," he said in the media statement.