Antibiotics and Breast Cancer—What's the Meaning of This?

Breast cancer is the most frequent cancer diagnosed among women in the United States. Established risk factors include age, family history, reduced parity, earlier age at menarche, alcohol use, postmenopausal adiposity, and hormone therapy. In this issue of THE JOURNAL, Velicer and colleagues¹ report another potential risk factor: the use of prescribed antibiotics. Among 2266 women with breast cancer, as compared with 7953 controls, the use of antibiotics was more common; the risk of breast cancer was greater with longer duration of antibiotic use and was consistent across antibiotic classes. This observation is potentially worrisome in that antibiotic exposure is common and sometimes nonessential. Thus, if real, the risk of breast cancer attributable to the use of antibiotics could be large and partially preventable.