The research, conducted for the U.S. Preventive Services Task Force, involved reviewing all relevant studies found on the subject. Results appear in the July 2 issue of Annals of Internal Medicine, a medical journal, and coincide with release of a task force recommendation that women talk to their doctors about the issue.
"We looked for randomized, controlled trials of chemical prevention of breast cancer and found four in women without a previous diagnosis of that illness," said study leader Dr. Linda Kinsinger, assistant professor of medicine at the UNC School of Medicine. "Three of the four involved tamoxifen and one involved raloxifene, which the FDA has not approved yet. We also reviewed studies of the costs of drug treatment to prevent breast cancer and others assessing the risks of that treatment."
Conducted in the United States, the largest of the tamoxifen studies showed almost a 50 percent reduction in the risk of breast cancer among women with a higher than average chance of developing it within five years, Kinsinger said. It involved more than 13,000 women. The two other, smaller tamoxifen studies were conducted in Europe and did not reveal a statistically significant benefit.
"Only a few women in each of those trials took tamoxifen during the entire study period, and so that might be the reason there was no observed benefit," she said. "Other possible reasons were that the studies were small and shorter-term."
The raloxifene study, which focused on postmenopausal women with osteoporosis, showed a 76 percent reduction in relative risk.
"These are pretty substantial effects and are worth considering," said the physician, a member of the UNC Lineberger Comprehensive Cancer Center. "Unfortunately, the two drugs can have side effects, including some that are potentially serious. That creates something of a dilemma for patients and doctors when it comes to decision-making."
Both medications boost the risk of venous thromboembolic disease, which can cause blood clots in the legs or lungs, and hot flashes, she said. Tamoxifen appears to increase the risk of endometrial cancer and stroke slightly. Women who have their uteruses removed obviously do not have to worry about getting cancer there.
"It would be nice if we could say clearly that certain women should take one or the other of these drugs and that certain other women should not take them," Kinsinger said. "Unfortunately, life's usually not as simple as that, and what we've said -- that women should discuss this with their doctors and come to a decision together -- is the best we can advise, at least right now."
Indications for taking the drugs regularly include a family history of breast cancer, early menstruation, late or no childbirth and previous biopsies, even if they were negative, she said. Contraindications include previous blood clots, hypertension or diabetes.
Co-authors of the new research report are Drs. Russell Harris, associate professor of medicine at UNC; Steven H. Woolf, professor of family medicine at the Medical College of Virginia; Harold C. Sox, editor of Annals of Internal Medicine; and Kathleen N. Lohr, a chief scientist at RTI International, adjunct professor at UNC and head of the Evidence-Based Practice Center.
The team did not conduct a meta-analysis of the relevant studies, which would have entailed combining and re-analyzing all the data, since they felt the studies were not comparable enough, she said.
Like the other 11 AHRQ Evidence-based Practice Centers in the United States and Canada, the RTI-UNC team reviews all relevant information found on health topics to provide guidance for medical decisions. The U.S. Department of Health and Human Services' Agency for Healthcare Research and Quality supports the UNC and RTI work.
RTI International is an independent, nonprofit research organization dedicated to improving health and other human concerns. More information about it is available at http://www.rti.org/epc and about the U.S. Preventive Services Task Force at http://www.preventiveservices.ahrq.gov.
By DAVID WILLIAMSON
UNC News Services
Note: Contact Kinsinger via pager at (919) 216-1123, at (919) 843-6596, or lkins@med.unc.edu
AHRQ Contact: Barbara Najar, (301) 594-9881
RTI Contact: Reid Maness, (919) 541-7044
Journal
Annals of Internal Medicine