Study Finds Aspirin Use Not Associated With Lower Breast Cancer Death Risk

In addition to finding no association between aspirin use and reduced risk of breast cancer, researchers find non-breast cancer deaths higher among aspirin users.

Despite prior research that suggests use of aspirin can improve survival rates in certain types of cancer, a recent study finds that aspirin use is not associated with a lower risk of death from breast cancer.

Published online June 2, 2014, in BMC Cancer, the study found that aspirin intake in breast cancer patients is associated with a lower risk of death from the disease only in short term assessments. The study also found that death from causes other than breast cancer was higher among aspirin users.

“Because of these two findings, we speculate that the phenomenon of confounding by indication may be contributing to the conflicting results from prospective studies,” the study authors wrote.

Aspirin has been shown to be beneficial in the treatment of some cancers. For example, patients with colon cancer showed improved overall survival through aspirin therapy, according to a study published online on March 31, 2014, in JAMA Internal Medicine. Though the exact mechanism for aspirin’s effectiveness in fighting cancer has not been determined, researchers hypothesize it may come from preventing platelet-induced adhesion of circulating tumor cells that initiate metastases.

After examining prior data that suggest a protective effect from aspirin rivaling the benefits of current breast cancer therapies, researchers in the BMC Cancer study looked at aspirin use in a Swedish registry of 27,426 women diagnosed with breast cancer between 2005 and 2009.

The study employed a nested case—control design to examine aspirin use at varying time intervals, starting from 3 months following the initial diagnosis. Researchers found that 1661 women in the registry died from breast cancer, with a median follow-up of 2.57 years. An additional 1371 women died from other causes.

Of the women in the study, 12.6% had severe comorbid conditions that were associated with recommendations to use or not use aspirin.

Researchers determined the use of aspirin was associated with a reduced risk of breast cancer death only when it was assessed in the short term without any delay, for example, in the 6-month period preceding death. The use of nonsteroidal anti-inflammatory drugs was found to correlate with an increased hazard of breast cancer death due to increased usage for pain management as patients moved closer to dying, according to the study.

An increased risk of death from other causes in aspirin users could be a result of aspirin being taken as secondary prevention for cardiovascular disease, the study noted.

“A randomized trial will be the only way to sort out the issues of confounding by indication, balance the risk of mortality from bleeding versus a potential benefit on breast cancer survival, and determine a causal relationship between breast cancer prognosis and ASA [aspirin],” the authors wrote.