A provocative new study suggests that aspirin reduces the odds of death in breast cancer survivors, although doctors caution it is too soon to know if women should start taking the drug as soon as they are diagnosed.
The research, part of the long-running Nurses' Health Study, followed 4,164 female nurses who had been diagnosed with early stage breast cancer. Harvard investigators found that nurses who took aspirin -- usually to protect against heart disease -- were 50 percent less likely to have their cancer spread and 50 percent less likely to die from breast cancer.
"This is a very interesting and exciting study that suggests aspirin may reduce the recurrence of breast cancer," said Dr. Richard Besser, senior health and medical editor for ABC News. "However, the design of the study does not allow for definitive conclusions. Hopefully, there will be randomized trials of aspirin use to answer this question."
The study appears in the latest issue of the Journal of Clinical Oncology.
The risk in drawing too heavily on the current study is that women who were taking aspirin were doing so of their own volition and were not assigned randomly to take it by researchers. Therefore, it is possible that the women taking aspirin had something else in common that would account for their lower breast cancer mortality.
"We can't prove [at this point] that aspirin improves survival in women with breast cancer," said Dr. Michelle Holmes, the study's lead author. "You shouldn't just start taking aspirin because of this for sure." But, she said, "If you're taking it for other reasons, you might be helping yourself in this way, too."
A randomized controlled trial will be necessary for doctors to know if it was the aspirin itself that accounted for the difference.
"As noted by the study authors, it is possible that survival results could have been influenced by women with recurrent breast cancer being advised to stop taking aspirin during chemotherapy, resulting in an overestimate of any benefit of aspirin use," said Eric Jacobs, strategic director of pharmacoepidemiology for the American Cancer Society.
"The study also suggested regular aspirin use might reduce risk of breast cancer recurrence. However, the date of breast cancer recurrence sometimes needed to be estimated rather than being known, and it is unclear how this might have influenced results," he said.
Researchers speculate that aspirin reduces inflammation and thus cuts cancer risk. Supporting this idea, women who regularly took other anti-inflammatory drugs, such as ibuprofen, also had a 50 percent lower risk for death from breast cancer.
Experts say the findings are intriguing and deserve further research. "An important report -- definitely," said Alan Kristal, an epidemiologist at the Fred Hutchinson Cancer Research Center in Seattle.
A Subject of Scrutiny
Adding some caution to the findings is that conclusions from the Nurses' Health Study have been famously wrong on a number of occasions.
Data from this study showed women who took hormone replacement therapy had lower rates of heart disease -- a finding that was not confirmed in a randomized study. Similarly, it showed that women who took vitamin E had lower rates of heart disease. Later research found this not to be true; vitamin E might even be harmful in large doses.
"The vitamin E story needs to humble us here," said Dr. Tim Byers, deputy director of the University of Colorado Cancer Center in Denver. "This is especially important as so many breast cancer survivors will be jumping at this... This will inevitably be a news story. Covering it with the right amount of uncertainty will be important."
Others agree that it could be dangerous if women started taking aspirin because of these findings. "Because frequent aspirin use can have serious side effects such as (occasionally fatal) gastrointestinal bleeding, it's not something I would want to encourage based on this study alone," said Sander Greenland, an epidemiologist at UCLA.
But while it may be too soon to take aspirin for breast cancer, there could be other reasons to take it.
"There are many women with heart disease for whom aspirin is recommended," said Besser. "It is worth speaking with your doctor to find out if you fall into that group."