Study calls into question recommendation to counsel all high-risk women about the drug

(SACRAMENTO, Calif.) -- Among women at high risk for breast cancer, fewer than one in five were inclined to take the drug tamoxifen to prevent the disease, according to researchers at the UC Davis School of Medicine and Medical Center. Concerns about the drug's potential side effects were the primary reason. The study, funded by the California Breast Cancer Research Program and the National Cancer Institute, will be published in the May 15 issue of CANCER, a peer-reviewed journal of the American Cancer Society.

Taking tamoxifen can reduce a woman's risk of developing breast cancer by as much as 49 percent. However, the drug also increases risks for endometrial cancer, deep venous thrombosis, pulmonary embolism, painful sexual intercourse and cataracts requiring surgery.

"The most important implication of our study is that even among women considered at high risk for breast cancer, and eligible to take a medication to reduce their risk, many are reluctant to do so," said Joy Melnikow, professor of family and community medicine at UC Davis and lead author of the study. "Women in our study were very concerned about potential harmful effects when they considered taking tamoxifen to reduce their risk for a disease they might not get."

The finding has implications for the development of other chemoprevention drugs to reduce cancer risk. "Potential harmful effects become much more important in the context of reducing risk for a potential disease, in contrast to treating a disease," Melnikow said. "To have successful risk-reducing agents for healthy people, it appears we will need agents with minimal side effects."

In the study, Melnikow and her colleagues interviewed 255 women with significant risk factors for breast cancer about their interest in taking tamoxifen to prevent the disease. Afterward, the women received a 15-minute counseling session about the risks and benefits of tamoxifen therapy for breast cancer prevention, followed by an evaluation of their knowledge about the drug and their willingness to take it.

The percentage of women inclined to take tamoxifen was the same before and after the education session -- 19 percent. Ten women who had been inclined against tamoxifen beforehand were inclined to try it afterward, but nine women who had been inclined to take the drug initially changed their minds when they learned more about the risks and benefits.

The U.S. Preventive Health Services Task Force in 2002 recommended that doctors discuss chemoprevention with women at high risk for breast cancer. An estimated 10 million women in the United States have significant risk factors for breast cancer that make them eligible for tamoxifen therapy to prevent the disease.

The UC Davis study calls into question the recommendation to counsel so many women. "Given the very small number of women whose decision was influenced by the educational session in our study, this recommendation may be unrealistic," Melnikow said.

The study was designed to understand how women make the decision to take or not take tamoxifen. "We found that a lot of women were not as afraid of breast cancer as we thought they would be, and that surprised us," Melnikow said. "We thought we would see generalized fear about breast cancer and a willingness to do anything to prevent it. Instead, many of the women viewed breast cancer as just another chronic disease, and no worse than some of the potential adverse effects of tamoxifen, such as pulmonary embolism."

Tamoxifen is a synthetic estrogen receptor modulator originally derived from the bark of the Pacific yew tree. It is used in breast cancer treatment as well as prevention.

Melnikow is an author of nearly 40 peer-reviewed scientific articles examining how women make medical decisions, cancer prevention strategies, maternal-child health issues in underserved populations, and the cost-effectiveness of various aspects of women's health care, among other topics in primary care. She received her medical degree from the University of California San Francisco and completed her family practice residency training at the University of Massachusetts. She also holds a master’s degree in public health.

UC Davis Cancer Center is the only National Cancer Institute-designated cancer center serving inland Northern California. It is a program of the University of California, Davis School of Medicine and Medical Center.