OBJECTIVES: Growing body evidence suggests that statins may decrease the risk of cancers. However, available evidence on breast cancer is conflicting. We therefore examined the association between statin use and risk of breast cancer by conducting a detailed meta-analysis of all observational studies published regarding this subject. METHODS: PubMed database and bibliographies of retrieved articles were searched for epidemiological studies published up to January 2012, investigating the relationship between statin use and breast cancer. Before meta-analysis, the studies were evaluated for publication bias and heterogeneity. Pooled relative risk (RR) and 95% confidence interval (CI) was calculated using random-effects model (DerSimonian and Laird method). Subgroup analyses, sensitivity analyses and cumulative meta-analysis were also performed. RESULTS: A total of 24 (13 cohort and 11 case-control) studies involving more than 2.4 million participants and 76,759 breast cancer cases contributed to this analysis. We found no evidence of publication bias and evidence of heterogeneity among the studies. Statin use and also long-term statin use did not significantly affect breast cancer risk (RR = 0.99; 95% CI = 0.94-1.04; P = 0.69 and RR = 1.03; 95% CI = 0.96-1.11; P = 0.42, respectively). When the analysis was stratified into subgroups, there was no evidence that study design, confounder’s adjustments and previous meta-analysis substantially influenced the effect estimates. Sensitivity analyses confirmed the stability of our results. Cumulative meta-analysis showed a change in trend of reporting risk of breast cancer from positive to negative in statin users between 1993 and 2011. CONCLUSIONS: Our meta-analysis findings do not support the hypothesis that protective effect of statins against breast cancer. More randomized clinical trials and observational studies were needed to confirm this association with underlying biological mechanisms in future.