These women are also less likely to die from their breast cancer.
The study of Irish patients funded by the Irish Health Research Board and Irish Cancer Society and published by the American Association for Cancer Research in the Journal, Cancer Research
, analyses records from the National Cancer Registry Ireland (NCRI), and prescription data from the General Medical Service (GMS) pharmacy claims database.
"Our findings suggest that aspirin could play a role in reducing mortality from breast cancer by preventing the cancer spreading to nearby lymph nodes", said Dr Ian Barron, the lead author who carried out the research at Trinity College Dublin, and is now working at Johns Hopkins, USA.
"We analysed data from 2,796 women with stage I-III breast cancer. We found that those women prescribed aspirin in the years immediately prior to their breast cancer diagnosis were statistically significantly less likely to present with a lymph node-positive* breast cancer than non-users. The association was strongest among women prescribed aspirin regularly and women prescribed higher aspirin doses. We now need to establish how and why this is the case".
The findings are consistent with two other major studies. The first is an analysis of cardiovascular trials where pre-diagnostic aspirin** use was associated with a statistically significant reduction in the risk of developing metastases and dying from cancer.
The second is an observation from in vivo breast cancer models, which suggest a possible mechanism by which aspirin may reduce the risk of cancer spreading to other parts of the body.
Professor Kathleen Bennett, a co-author from the Department of Pharmacology & Therapeutics, School of Medicine, Trinity College Dublin said: "Our study was observational and these results do not mean that women should start taking aspirin as a precautionary measure. Aspirin can have serious side effects. We still need to identify exactly how aspirin may prevent breast cancer from spreading to the lymph nodes; which women, or types of breast cancer, are most likely to benefit from taking aspirin; as well as what the optimum doses might be. Research to help answer the next questions is funded by the Irish Cancer Society as part of its first National Collaborative Cancer Research Centre, BREAST-PREDICT".
Dr Graham Love, Chief Executive of the Irish Health Research Board said: "These results have great potential to help improve our understanding of how to increase Irish and global survival rates from breast cancer."