Statin Use and Breast Cancer: Prospective Results From the Women's Health Initiative

Background: Despite experimental observations suggesting that 3-hydroxy-3-methylglutaryl coenzyme A inhibitors (statins) have antitumor activity, clinical studies have reached mixed conclusions about the relationship between statin use and breast cancer risk. Methods: To investigate associations between potency, duration of use, and type of statin used and risk of invasive breast cancer, we examined data for 156 351 postmenopausal women who were enrolled in the Women's Health Initiative. Information was collected on breast cancer risk factors and on the use of statins and other lipid-lowering drugs. Cox proportional hazards regression was used to calculate hazard ratios (HRs) with 95% confidence intervals (CIs). Statistical tests were two-sided. Results: Over an average follow-up of 6.7 years, 4383 invasive breast cancers were confirmed by medical record and pathology report review. Statins were used by 11 710 (7.5%) of the cohort. Breast cancer incidence was 4.09 per 1000 person-years (PY) among statin users and 4.28 per 1000 PY among nonusers. In multivariable models, the hazard ratio of breast cancer among users of any statin, compared with nonusers, was 0.91 (95% CI = 0.80 to 1.05, P = .20). There was no trend in risk by duration of statin use, with HR = 0.80 (95% CI = 0.63 to 1.03) for