Q: Are antibiotics another risk factor for breast cancer?

Ask Our Expert About Antibiotic Use and Breast Cancer

About Our Expert

Gregory R. Harper, MD, Ph.D., is medical director of Breast Health Services and the Cancer Risk and Genetic Assessment Program at Lehigh Valley Health Network. Voted one of the Best Doctors in America three times, Harper is known as a compassionate physician who provides patients with the right balance of information and hope.

Q: Are antibiotics another risk factor for breast cancer?

A: Not necessarily! The Journal of the American Medical Association has reported a study linking high use of antibiotics with increased risk of breast cancer.

The use of antibiotics, which can change the bacterial environment of the intestinal tract, has been theorized to affect cancer risk by disrupting the protective effect of bacteria on food products that could potentially be cancer causing. Reported in the February 18th issue of JAMA is a study from the University of Washington, Seattle, which describes an association between use of antibiotics and increased risk of breast cancer. The risk increased with increasing use of antibiotics, up to a doubling of risk for women who had more than 25 antibiotic prescriptions or who took antibiotics for at least 501 days over an average of about 17 years.

Before women stop taking antibiotics appropriate to the infection being treated, it is important to understand the limitations of this study. First, the group with increased numbers of breast cancer also had an increase in the number of women at risk for developing breast cancer in the first place. These risk factors include:

• higher education status
• use of oral contraceptives
• early first menstrual periods
• having first child over 30 years of age
• positive family history of breast cancer
• obesity

Second, the study reported lower mammography rates among the control group, which could have underestimated the number of breast cancers because they were not detected prior to the study. Third, the study reports an association, not a cause and effect.

Studies of this type are important because they raise questions that will be tested in the future. However, additional research will be required to confirm the results found in this observation.

Luther Rhodes, M.D., Lehigh Valley Health Network's chief of infectious diseases, has also carefully reviewed the studies just published on antibiotics and possible risk for breast cancer. He is very concerned that people who have breast cancer or are worried about a reoccurrence of cancer might assume that a recent or past course of antibiotics will put them at risk of cancer. The medical science on this topic if far from conclusive . The studies just published are an important avenue for further study, but are not intended to be the final word. Just a few years ago, there were articles trumpeting an association of coffee consumption and various cancers which caused cancer patients ( and coffee drinkers) allot of anxiety and guilt. Those articles have subsequently been proven false. The message for patients today is not to use a fear of cancer as a reason not to take a necessary antibiotic. Discuss your concerns with your physician or nurse practitioner.

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