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Antibiotic Use Is Linked with Breast Cancer Risk

But we don't know why.

Several theories posit a biologically plausible connection between antibiotic use and cancer risk, potentially through drug effects on hormones or cancer-protective compounds. To assess whether such a connection actually exists, researchers conducted a population-based, observational study of 2266 women with newly diagnosed primary, invasive breast cancer (cases) and 7953 randomly selected age-matched women without breast cancer (controls) in a Seattle-area health plan. The plan's pharmacy database was used to determine the cumulative number of days of antibiotic use before breast cancer diagnoses (cases) or matched reference dates (controls).

Antibiotic use was significantly associated with breast cancer risk at all levels of antibiotic use (from 1-50 days to 1001 days) and for all drug classes. For example, odds ratios were 2.07 for overall antibiotic use of more than 1000 days and 2.26 for macrolide use of more than 100 days (compared with no use). For all levels of use and for most drug classes, there was an even stronger association with risk for death from breast cancer than with risk for breast cancer overall (maximum OR, 5.75).

Comment: Publicity about this study will prompt many questions from patients. However, the reason for the observed association between antibiotic use and breast cancer risk remains unclear. According to the editorialists, possible explanations include confounding by unknown variables, effects of the inflammatory disorders for which antibiotics were prescribed, or carcinogenic effects of the antibiotics themselves.

— Thomas L. Schwenk, MD

Published in Journal Watch General Medicine February 27, 2004

Citation(s):

Velicer CM et al. Antibiotic use in relation to the risk of breast cancer. JAMA 2004 Feb 18; 291:827-35.

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• Medline abstract (Free)

Ness RB and Cauley JA. Antibiotics and breast cancer -- What's the meaning of this? JAMA 2004 Feb 18; 291:880-1.

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• Medline abstract (Free)