Aspirin use and breast cancer risk: a meta-analysis and meta-regression of observational studies from 2001 to 2005

Purpose To examine the recent epidemiological studies on aspirin use and breast cancer risk published from 2001 to 2005 within a meta-analysis, to investigate reasons for heterogeneity between the individual studies and to analyse a dose-response-relationship considering frequency and duration of use. Methods We systematically searched for cohort-studies and case-control-studies from 2001-2005, which evaluated the association between aspirin and breast cancer risk. We calculated a pooled estimate for the relative risk (RR) and investigated reasons for heterogeneity between the individual studies and analysed a dose-response-relationship using random effects mixed models. Results We identified 10 studies which met the inclusion criteria. The combined estimate of the RR was 0.75 (95%CI: 0.64, 0.88) using the random effects model. Heterogeneity between the studies could not be explained by the covariates study-type and study-population. The combination of frequency and duration of aspirin use resulted in a significant dose-response-relationship between aspirin use and breast cancer risk. Each additional pillyear reduced the breast cancer risk to about 2%. Conclusion Our meta-analysis supports the current evidence that aspirin may reduce breast cancer risk. Moreover, a dose-response-relationship seems to exist. However, results have to be interpreted carefully, as exposure categories were defined very heterogeneously among the studies which weakens the validity of the pooled estimates. Copyright (C) 2007 John Wiley & Sons, Ltd.