Does Antibiotic Use Cause Breast Cancer?
Antibiotic Use and Breast Cancer Risk
You may have seen or heard the recent news reports on a possible link between antibiotic use and breast cancer risk. These reports are based on a study published in the February 18, 2004 issue of the Journal of the American Medical Association, which found that women who had more than 25 antibiotic prescriptions over an average period of 17 years were significantly more likely to develop breast cancer than women who never took them.
If you take or have taken antibiotics, you may be concerned that you have put yourself at greater risk for breast cancer. But experts say that it is too early for such concerns. Study coauthor Stephen Taplin, MD, of the National Cancer Institute's Division of Cancer Control and Population Sciences, stressed that the results do not necessarily mean that antibiotics cause breast cancer. Rather, they simply mean that researchers have found an important association worthy of further investigation.
"This is not a reason to feel scared or to stop taking antibiotics," Dr. Taplin said. "None of us believes that it is anything more than a very interesting finding that needs to be looked at more carefully. It's a clue to where we might look to find more answers."
The study's lead author, epidemiologist Christine Velicer, PhD, Dr. Taplin, and a team of other researchers compared nearly 3,000 women with breast cancer who were enrolled in the Group Health Cooperative health plan in Seattle with nearly 8,000 plan members who did not have breast cancer. They found that women who took antibiotics for more than 500 days -- or had more than 25 prescriptions -- over an average period of 17 years had more than twice the risk of breast cancer as women who had not taken any antibiotics. The authors found an increased risk in all classes of antibiotics that they studied. "One of the main questions now is whether the antibiotics themselves, or the underlying conditions that lead to antibiotic use, are increasing breast cancer risk," says Dr. Taplin.
It may be that women with a tendency to develop bacterial infections treated by antibiotics are also more susceptible to the development of cancer. On the other hand, the antibiotics themselves are known to affect certain bodily processes -- such as the immune response, and the absorption of cancer-fighting chemicals in food -- and one or more of these effects may raise breast cancer risk. Future studies will be needed to explore these possibilities.