"I think that there's still additional work that needs to be done before recommending daily aspirin use for breast cancer prevention," researcher Gretchen Gierach, PhD, tells WebMD.
"If aspirin is truly a risk-reducing approach, it would be very exciting since we have few ways to prevent breast cancer, but we need additional studies," says Gierach, a cancer prevention fellow at the National Cancer Institute.
Women who are wondering what to do in the meantime should keep in mind the potential risks of daily aspirin use, which include gastrointestinal bleeding. "I'm not a physician, so I would recommend that any woman would speak to her physician before beginning any new regimen," says Gierach.
Aspirin and Breast Cancer Study
Gierach's new study, published online in Breast Cancer Research, is based on data from more than 127,000 U.S. women.
When the study started in 1996-1997, the women were 50-71 years old and had no history of cancer. They were asked how often they had used aspirin or other over-the-counter nonsteroidal anti-inflammatory drugs (NSAIDs).
The women were followed through December 2003. During that time, a total of 4,501 women were diagnosed with breast cancer.
Overall, NSAID use wasn't associated with breast cancer risk. But women who reported taking daily aspirin were 16% less likely to develop estrogen-receptor positive breast cancer. Those tumors are fueled by estrogen; most breast cancers are estrogen-receptor positive.
NSAIDs, which include aspirin, "are hypothesized, through a cascade of events, to potentially reduce estrogen synthesis in the body, so that might be one explanation for the reduced risk we saw for estrogen-receptor positive breast cancers," Gierach explains.
So why did aspirin stand out in the study? That's not clear, but Gierach notes that "aspirin is unique from other NSAIDs in how it behaves in the body."
The study has some limits. For instance, it doesn't show how long the women took aspirin or other NSAIDs, what doses they took, why they took aspirin or other NSAIDs, or whether they were taking prescription NSAIDs.
The dosing information "might be important, because previous studies have seen different effects for low dose vs. regular dose aspirin," says Gierach.
On-Again, Off-Again Findings
This isn't the first study to look at breast cancer, aspirin, and other NSAIDS -- and past studies have had mixed results.
In March 2008, British researchers reported that regular use of aspirin -- and possibly other NSAIDs -- might cut breast cancer risk by up to 20%.
And in 2004, other researchers reported in The Journal of the American Medical Association that taking aspirin might lower women's risk of developing hormone-sensitive breast cancers.