Statin use and risk of breast cancer among women with benign breast disease: a Danish nationwide cohort study

Background: Statins have been suggested to protect against breast cancer risk, but the observational evidence is inconclusive. We examined the association between statin use and breast cancer incidence among women at higher risk of breast cancer due to a history of benign breast disease (BBD). Methods: Using Danish registries, we identified cancer-free women aged >= 50 years during 1996-2018 with a history of BBD and no prior statin prescriptions. Using Cox regression, we estimated multivariable-adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) for invasive breast cancer through 2020 with time-varying statin use defined according to continuity, duration, and intensity (estimated average daily dose), derived from prescription data. Results: Among 111,550 women, 7629 were diagnosed with breast cancer during median follow-up of 12.2 years. Overall statin use was not associated with breast cancer incidence (adjusted HR = 0.99; 95% CI, 0.93-1.06), with similar associations observed according to continuity and duration of use. However, long-term (>= 10 years), high-intensity statin use was associated with a reduced HR of 0.75 (95% CI, 0.60-0.96). Conclusions: Our findings did not indicate an association for overall statin use with breast cancer incidence among women with BBD. The inverse association with long-term, high-dose statin use requires further evaluation.