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.