Use of antibiotics and risk of breast cancer.

A recent nested case-control study found that increasing use of antibiotics was associated with a significantly elevated risk of breast cancer. The authors attempted to replicate this finding with a similar study design using the General Practice Research Database in the United Kingdom. Women aged 30-79 years who were registered in the database between January 1995 and December 2001 comprised the study cohort. A total of 3,708 women with incident cases of breast cancer and 20,000 frequency-matched controls were entered into a nested case-control analysis. Use of antibiotics was not associated with an increased risk of breast cancer. For categories of increasing cumulative days of use (1-50, 51-100, 101-500, and >or=501 days), the corresponding odds ratios were 1.0 (95% confidence interval (CI): 0.9, 1.1), 1.0 (95% CI: 0.8, 1.1), 0.9 (95% CI: 0.7, 1.0), and 1.2 (95% CI: 0.9, 1.6) (p = 0.31 for trend). On the basis of these results, antibiotic use does not appear to be a major determinant of breast cancer risk.