MONDAY, March 22, 2004 (HealthDayNews) -- The drug tamoxifen has been shown to cut breast cancer risk by nearly 50 percent, yet many women at high risk of the disease are not taking the medication.

A study in the March 22 online edition of Cancer finds only 63 percent of women were offered the drug and only 26 percent accepted it. The authors believe physician practices and the attitudes of at-risk women are responsible for the low rates of tamoxifen use.

Breast cancer is the most common cancer among women, except for skin cancer, says the American Cancer Society. While death rates from breast cancer have been declining, it is still the second leading cause of cancer death among women, after lung cancer.

Tamoxifen, which has been on the market since 1978 for treating breast cancer, was approved in 1998 for women at high risk of developing the disease.

The U.S. Food and Drug Administration based its approval on a National Cancer Institute (NCI) study of more than 13,000 women believed to be at increased risk of breast cancer. The trial was halted 14 months early when interim results showed tamoxifen slashed the incidence of breast cancer by nearly one half.

Tamoxifen works by blocking cancer cell multiplication, but it can cause potentially bothersome side effects, such as hot flashes, irregular periods, vaginal dryness and the need to use a barrier form of birth control. It also is linked to increased risk of blood clots, endometrial cancer and eye problems.

So far, there has been little data on tamoxifen's use in clinical settings. Researchers at Northwestern University reviewed records from 219 women who were seen at the Lynn Sage Breast Center for risk evaluation in the wake of the pivotal NCI study. Their hope was to identify markers that would predict the drug's use.

Two risk factors stood out as significant predictors. Women with a history of atypical hyperplasia -- a noncancerous condition that indicates higher risk for breast cancer -- or lobular carcinoma in situ -- a precancerous condition -- were twice as likely to be offered and accept tamoxifen therapy as women without those risk factors.

In general, if a woman is being offered tamoxifen, she is at increased risk of breast cancer and is likely to enjoy a greater net benefit from the drug, the authors report.

However, among premenopausal women who could benefit from the drug, only 55 percent were offered tamoxifen and only 36 percent accepted it. By contrast, 72 percent of postmenopausal women were offered the drug and 46 percent accepted it.

Dr. Henry M. Kuerer, director of the Breast Surgical Oncology Training Program at the University of Texas M.D. Anderson Cancer Center, says that while patients need to hear the potential benefits and risks, the decision to take tamoxifen is a personal one.

"They're not universally taking a pill just because on the surface it sounds like they are going to decrease their chance of developing breast cancer," he insists.

More information

The National Cancer Institute has more information on breast cancer and tamoxifen.

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