Posted: Dec 14, 2010 9:05 PM
Their study of 116,181 women suggests that those aged 51 to 70 gain the greatest benefit, says Boikanyo Makubate, PhD, of the University of Dundee.
U.S. doctors caution that it's too soon to recommend that women take aspirin in an effort to ward off breast cancer.
The study showed that women who took aspirin for three to five years were 30% less likely and women who took it for more than five years were 40% less likely to develop breast cancer.
When the researchers looked at how often a woman took aspirin, only taking the painkiller more than twice a week was associated with a substantial 40% reduced risk of breast cancer.
When looked at by age, women aged 51 to 60 and women aged 61 to 70 had a 56% and 43% reduction in risk, respectively.
The findings were presented at the San Antonio Breast Cancer Symposium.
Although provocative, the study only shows an association and does not prove cause and effect, says Steven Isakoff, MD, PhD, a breast cancer specialist at Massachusetts General Hospital Cancer Center in Boston.
Still, if the findings can be confirmed in a large study in which half the women are given aspirin and half aren't and all are followed over time to see how many in each group develop breast cancer, the painkiller could have a huge impact, particularly in underdeveloped nations, Isakoff says.
"As a public health measure, aspirin is cheap and easy," he says.
Makubate says the previous studies looking at aspirin use in breast cancer have had conflicting results.
Laboratory work at his institution suggests aspirin could have an effect on breast cancer by blocking the Cox-2 enzyme that promotes inflammation and cell growth.
So Makubate and colleagues combed the medical records of British women aged 25 and older who were cancer-free in 1998. By the end of 2003, 1,420 (1.2%) developed breast cancer.
Prescription records showed one in five women took aspirin during the study period.
All the analyses were adjusted to take into account a woman's age and socioeconomic status, both of which affect breast cancer risk. But the researchers did not take into account other information, such as family history, that have an impact on risk.
Also, the researchers did not look at what dosages may work best.
A strength of the study is that prescribing records, not faulty memories, were used to gather information on aspirin use, Isakoff says.
This study was presented at a medical conference. The findings should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.