Tamoxifen not likely to prevent many breast cancers in at-risk women

Research has shown that the drug tamoxifen citrate not only helps prevent recurrence of breast cancer, but it also can keep the deadly disease from occurring in the first place in some women.

But a new University of North Carolina at Chapel Hill study indicates it’s unlikely that tamoxifen will ever be given widely to women to prevent breast cancer. That’s because the drug would avert only a maximum of 6 percent to 8.3 percent of breast tumors in eligible women, UNC School of Medicine researchers have found. “Our calculations showed that tamoxifen’s possibly harmful side effects, including blood clots and stroke, would rule out some 90 percent of women who might benefit from taking it each day,” said Dr. Russell P Harris, associate professor of medicine at UNC. A report on the study appears in the latest issue of the Archives of Internal Medicine.

Besides Harris, a member of UNC’s Lineberger Comprehensive Cancer Center, authors are principal investigator Dr. Carmen L. Lewis, assistant professor of medicine at UNC; Dr. Linda S. Kinsinger, assistant director of the VA Center for Health Promotion and Disease Prevention; and Robert J. Schwartz, a computer programmer at UNC’s Cecil G. Sheps Center for Health Services Research.

The study involved having 605 women, ages 40 to 69, in 10 general internal medicine practices in North Carolina, fill out questionnaires about their health and family histories of breast cancer. Then, using a proven formula for assessing breast cancer incidence and factoring in the women’s responses, researchers determined the expected number of cases that would occur over the next five years.

They found that only a relatively small number of women in primary care practices would be eligible for the chemopreventive therapy because of existing conditions such as high blood pressure and diabetes and other risk factors, Harris said. Since the majority of women never develop breast cancer anyway, the percentage of actual cancers prevented would be small.

“Screening mammography, which is useful, is not the whole answer to preventing breast cancer deaths, and our new work shows that tamoxifen won’t be either,” he said. “On the other hand, in a message to the research community, tamoxifen has shown us that if we can find other chemopreventive agents that don’t have all the side effects, then we could have greater success and save more lives.”

Tamoxifen works in women by blocking what’s known as the estrogen receptor that allows the hormone to work, the physician said. Most breast cancer development is dependent on estrogen.

Limitations of the research were that the number of women in each age category of the overall group were small, and black women, women with less education and those with no health insurance were not well represented in the sample, Harris said. Similar studies with larger numbers of subjects would help confirm the results.