Study Shows Link Between Antibiotic Use and Increased Risk of Breast Cancer

A study published recently in the "Journal of the American Medical Association" (JAMA) shows that use of antibiotics is associated with an increased risk of breast cancer — the more antibiotics the women in the study used, the higher their risk of breast cancer. The results of the study do not mean that antibiotics cause breast cancer.

The authors, who are from Group Health Cooperative (GHC) in Seattle; National Cancer Institute (NCI), part of the National Institutes of Health (NIH); University of Washington, Seattle; and the Fred Hutchinson Cancer Center, also in Seattle, 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 risk was smaller for women who took antibiotics for fewer days. However, even women who had between one and 25 prescriptions over an average period of 17 years were about 1.5 times more likely to be diagnosed with breast cancer than women who didn't take any antibiotics. The authors found an increased risk in all classes of antibiotics that they studied.

While the authors said that much more study is needed, possible explanations for the association could be how antibiotics affect bacteria in the intestine, or on antibiotics' effects on the body's immune response and response to inflammation, or perhaps that the conditions that led to the antibiotics prescriptions caused the increased risk, or that a weakened immune system is the cause of this association.

Additionally, breast cancer risks could differ between women who take low-dose antibiotics for a long period of time and women who take high-dose antibiotics only once in a while.

Over the past decade, overuse of antibiotics has become a serious problem. Efforts such as the "Get Smart: Know When Antibiotics Work" campaign unveiled last year by the CDC and the Food and Drug Administration (FDA) and other partners aim to lower the rate of antibiotic overuse.

To view Questions and Answers about this study, please go to www.cancer.gov/newscenter/pressreleases/AntibioticsQandA

To learn more about the "Get Smart: Know When Antibiotics Work" campaign, go to www.cdc.gov/drugresistance/community.