In addition to breast exams and mammograms, some doctors have suggested that women could take the drug tamoxifen to ward off breast cancer. But, like any drug, tamoxifen has risks; in one study, women taking tamoxifen to prevent breast cancer were more likely to get endometrial cancer and have strokes. That means the drug is probably best for the women most likely to be helped by the drug and least likely to experience the worst side effects. Researchers in North Carolina took a stab at finding out how many women are in that category.

What the researchers wanted to know: How many women are good candidates to take tamoxifen to prevent breast cancer?

What they did: Ten internal-medicine practices in central North Carolina agreed to take part in the study. Research assistants spent six days in each practice, approaching 40-to-69-year-old women in the waiting room and asking each to fill out a short questionnaire. The questionnaire asked about women's risk factors for breast cancer, such as whether they'd ever had an abnormal biopsy and whether any close relatives had had breast cancer, and about factors that would increase the risk of taking tamoxifen, including diabetes or having had a hysterectomy. They excluded women who'd had breast cancer or colon cancer, since the study was about preventing cancer. "Increased risk" was defined as a 1 in 60 or greater chance of getting breast cancer in the next five years.

What they found: Researchers found that, at the most, 10 percent of women in these medical practices could be candidates for tamoxifen—those were the women with an increased breast cancer risk and a low risk for adverse events from tamoxifen. The number of women with increased risk of breast cancer varied by age and race, from 3 percent of black women and 9 percent of white women in their 40s to 13 percent of black women and 53 percent of white women in their 60s.

What the study means to you: Tamoxifen may help prevent breast cancer in some women—but not all that many.

Caveats: This study was carried out in 10 practices in one small geographic area, and most of the women were white, well-educated, and had health insurance. But this does provide some information for doctors to estimate how many of the women who walk through their door might be candidates for tamoxifen, if their practices look like this one.

Find out more: The National Cancer Institute has a fact sheet on tamoxifen, which was originally used to treat breast cancer, not to prevent it.

Read the article: Lewis, C. L., et al. "Breast Cancer Risk in Primary Care." Archives of Internal Medicine. Sept. 27, 2004, Vol. 164, pp. 1897–1903.

Abstract online: http://archinte.ama-assn.org