A JAMA study reports that women who had taken between one and 25 antibiotic prescriptions over an average of 17 years had an increased risk for breast cancer. The results do not mean women should stop taking antibiotics but that these medicines should be used wisely.
Velicer, CM, et al. “Antibiotic Use in Relation to the Risk of Breast Cancer.” JAMA.February 18,2004. 291 ():827-835.