Can Aspirin Really Increase Survival in Breast Cancer?

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A new study from reported online in the Journal of Clinical Oncology suggests that an aspirin at least two days a week can significantly reduce the risk of breast cancer death by 64% to 71% and reduce the risk for distant metastasis in breast cancer survivors by 43% to 60%.

Before anyone gets too excited about aspirin and its use in breast cancer patients, it needs to be remembered that the information comes from an observational study not a trial. Observational studies can not prove cause and effect.

Observational studies can point to a strong statistical association in large studies, but can not establish benefit.

Michelle D. Holmes, MD, DrPH, of the Channing Laboratory at Harvard and Brigham and Women's Hospital in Boston, and colleagues looked at data on 4,164 women taking part in the Nurses' Health Study. Participants were from all over the US and had been diagnosed with stage I, II, or III breast cancer between 1976 and 2002 and were followed until June 2006, or their death, whichever came first.

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They researchers analyzed self-reporting of aspirin intake for any links between breast cancer mortality risk and days per week of aspirin use (measured as 0, 1, 2 to 5, or 6 to 7 days per week). The study does not contain any information on aspirin dose, although the authors suggest “most regular use was likely for heart disease prevention at the 81 mg/day level.”

The results of this observational study noted that aspirin use was linked to a decreased risk of dying from breast cancer, showing a significant linear trend (the more days of aspirin use per week, the lower the risk of dying) even after adjusting for potential confounders (including demographics and diet), compared to no use at all. The relative risk (RR) of dying from breast cancer after taking aspirin on 1 day per week was 1.07; for 2 to 5 aspirin days per week it was 0.29, and for 6 to 7 aspirin days per week it was 0.36.

A similar relationship was noted for risk of distant recurrence of breast cancer. For distant recurrence, the adjusted RRs for 1, 2 to 5, and 6 to 7 days per week of aspirin use were respectively: 0.91, 0.40, and 0.57.

Aspirin use isn't risk-free. It can cause GI bleeding. It is important to remember that this is an observational study and can not prove cause and effect. These suggested findings will need to be confirmed in additional clinical trials.

Source reference:
Holmes MD, et al "Aspirin intake and survival after breast cancer" J Clin Oncol 2010; 28.

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