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Study: Few Women Benefit From Tamoxifen

Researchers Find Only Small Number of Women Benefit From Tamoxifen for Breast Cancer Prevention

WebMD Health News

Sept. 27, 2004 -- Few women at risk for breast cancer will benefit from taking the drug tamoxifen to reduce their risk, according to a new study.

Tamoxifen has been approved by the FDA for breast cancer prevention in women over 35 years old who are at increased risk of developing breast cancer in the next five years, according to a standard breast cancer risk estimation method used by doctors.

That approval came after a national study showed that the use of tamoxifen prevented nearly half of the breast cancers otherwise expected to occur in healthy women at high risk.

But the same study also showed that tamoxifen increased the risk of endometrial cancer, blood clots in the legs, dangerous blockage of arteries in the lungs (pulmonary embolism), and stroke.

Keeping the potential risks and benefits in mind, researchers say it's unclear how many women might be eligible for the breast cancer prevention drug and meet both requirements of increased breast cancer risk and low risk of side effects.

Few May Benefit From Breast Cancer Prevention Drug

In their study, published in the Sept. 27 issue of Archives of Internal Medicine, researchers surveyed 605 women aged 40 to 69 who visited an internal medicine practice in North Carolina in 2000.

Researchers used the survey to estimate the women's five-year breast cancer risk and then determine their eligibility for tamoxifen by looking at their risk of side effects from the drug. Women with a history of high blood pressure, diabetes, or blood clots in legs and/or lungs are considered at increased risk for adverse effects caused by tamoxifen.

The study showed that among white women, 9% of those in their 40s, 24% of those in their 50s, and 53% of those in their 60s were at increased risk for breast cancer within the next five years. Among black women, nearly 3% of those in their 40s, 7% in their 50s, and 13% in their 60s met the same requirement.

But when researchers considered the risk of side effects from tamoxifen in white women, they found 10% or fewer in all age groups were considered appropriate candidates for the drug based on their risk/benefit profile.

Among white women, the estimated maximum percentage of breast cancers that would be prevented if all these women adhered to taking their medications for five years was 6%-8%.

Based on those results, researchers say a relatively small number of women who visit primary care doctors may be eligible for discussing the use of tamoxifen to reduce breast cancer risk.

"Challenges lie in targeting discussions to the most appropriate women and in finding new [drug] prevention strategies that have less risk of harm," write researcher Carmen L. Lewis, MD, MPH, of the University of North Carolina at Chapel Hill, and colleagues.

SOURCES: Lewis, C. Archives of Internal Medicine, Sept. 27, 2004; vol 154: pp 1897-1903. WebMD Medical News: "Millions Could Benefit From Tamoxifen."

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