The concept of “chemoprevention” of breast cancer appeals to women, but that appeal may be based on an overestimation these women have of their own risks for the disease, say the authors of a report in a recent issue of Archives of Internal Medicine,(Vol. 161: 1639-1644).

In an era when pharmaceutical companies market prescription drugs directly to consumers, women should carefully weigh the benefits and risks of tamoxifen, approved by the FDA to prevent breast cancer in women at high risk, says the lead author. For example, certain women who take tamoxifen may face a higher risk of developing cancer of the uterus or forming blood clots in the leg that can travel to the lungs.

“This is not a benign drug,” says lead author Lori A. Bastian, MD, MPH, medical director for women’s health at the Durham Veterans Administration Medical Center in Durham, N.C., and assistant professor of medicine at Duke University.

Yet among the 1,273 women surveyed, 23% indicated they were interested in taking tamoxifen to prevent breast cancer, Bastian tells ACS News Today.

That’s a much greater percentage of women than those who might benefit from using tamoxifen to prevent breast cancer from developing in the first place, she says. Tamoxifen is a very useful drug to prevent recurrence of breast cancer in certain women who have had breast cancer surgery, and is useful in treating some women whose breast cancer has recurred.

Health care providers use an objective measure, called the Gail score, to assess a woman’s risk for breast cancer. A woman’s physician can help calculate a Gail score. A tool for this calculation, and how to interpret the score, can be found at the National Cancer Institute (NCI) website. The score is derived after a woman answers questions such as age (the older the woman, the higher the risk of breast cancer), whether she has had any children and starting at what age, and whether she has any “first degree” family members, such as mother, sister or a daughter who have the disease.

A Gail score of 1.66 is considered the threshold at which a woman may be able to reduce her cancer risk over the next five years by taking tamoxifen. The number means she would have a 1.66% or greater chance of developing breast cancer over the next five years.

Tamoxifen can have serious side effects, especially for certain women. In this study, women who in reality did not have a high risk of breast cancer indicated that they would consider chemoprevention, Bastian says. They perceived their chances of getting the disease as high, even when given the factual information to show otherwise, she says.

“Many researchers have found that women tend to overestimate their breast-cancer risk,” Bastian says. Now, her study indicates that overestimation can raise interest in chemoprevention.

This study grew from an earlier one looking at whether women take advantage of mammography, conducted by Barbara K. Rimer, DrPH, Bastian says. Rimer was at Duke University in Durham when she began the study, but now works for the NCI.

Bastian says the results of her study emphasize the need for health care providers to make sure they take the time to ask patients about their perceptions of breast cancer risk, figure out what the risk really is, and discuss the best way to prevent the disease or detect it early. Booklets, charts, and other “decision aids” should be tailored to patients’ risks, benefits, and concerns about breast cancer, she notes.

For most women, the effective course of action will be monthly breast self-exam, clinical breast examination by a health-care provider, and annual mammograms beginning at age 40, says Harmon Eyre, MD, chief medical officer and executive vice president for research and cancer control for the American Cancer Society.

“Physicians and patients need to have an informed decision-making interaction before deciding whether to take tamoxifen or not,” Eyre says. He explains that most of the tamoxifen prescribed today is for women who already have had breast cancer, as a treatment and prevention of recurrence.

While awareness of breast cancer can be a good thing if it spurs women to take the effective steps toward prevention, that doesn’t necessarily happen in practice, Bastian says. Some women may be so overly concerned that they put off mammography because they are afraid of what the test will show, she suggests.

But the good news is that more and more women are taking the steps toward prevention, Eyre says. The percentage of women over 50 who have had at least one mammogram is up to 80%, and 60% have one annually, Eyre says.

“That’s up dramatically from where it was 10 years ago,” he says. “Women are concerned and following up with behavior that is appropriate. Deaths from breast cancer are down by 17%. That translates to several thousand lives a year saved from premature death from breast cancer, due to early detection,” Eyre emphasizes.

For all the interest in chemoprevention, Eyre says, a large clinical trial funded by the NCI is still struggling to enroll thousands of women willing to take either tamoxifen or raloxifene, another drug believed to reduce breast cancer risk. Nearly all cancer centers across the country are participating and enrolling volunteers, he says.