Aspirin use and risk of breast cancer: systematic review and meta-analysis of observational studies.

Previous studies concerning the association between aspirin use and breast cancer risk yielded inconsistent results. We aimed to investigate the association by meta-analysis. PubMed and EMBASE were searched for relevant studies. We calculated the summary relative risks (RR) and 95% confidence intervals (CI) using random-effects models. Seventeen cohort studies and 15 case-control studies were included. The overall result showed that aspirin use decreased risk of breast cancer (RR, 0.90; 95% CI, 0.85-0.95). However, there was evidence of publication bias and heterogeneity and the association disappeared after correction using the trim-and-fill method. When stratified by study design, a significant benefit for aspirin users was only found in population-based and hospital-based case-control studies but not in cohort or nest case-control studies. Further subgroup analyses showed that aspirin use could decrease risk of in situ breast tumors or hormone receptor-positive tumors and reduce risk of breast cancer in postmenopausal women. Aspirin use may not affect overall risk of breast cancer, but decrease risk of in situ breast tumors or hormone receptor-positive tumors and reduce risk of breast cancer in postmenopausal women. Considering between-study significant heterogeneity and publication bias, confirmation in future studies is also essential. ©2015 American Association for Cancer Research.