Women who took aspirin every other day as part of a massive study had a lower rate of colon cancer after 15 years compared with women who didn’t follow this aspirin regimen, according to results published in the Annals of Internal Medicine. But colon cancer rates were the same after 10 years of study, suggesting that there may be a long lag before any cancer-protective effects of regular aspirin use appear. In addition, the women who took aspirin had higher rates of gastrointestinal bleeding than their counterparts.
Prophylactic use of aspirin has a long and controversial history. Daily aspirin use is often prescribed to individuals recovering after a heart attack or stroke to help prevent future cardiovascular events. But like all medical interventions, regular aspirin use carries some risk, such as the increased risk of ulcer or a well-documented association with gastrointestinal and cranial bleeding. More recently, one study suggested that regular aspirin use may increase the risk of developing macular degeneration. There is also debate about whether regular aspirin use might help prevent a first heart attack, but this practice has proved more controversial in light of the potential risks.
Some evidence suggests that daily aspirin use may reduce the risk of colon cancer, but 10-year follow-up data from the Women’s Health Study cast doubt on whether aspirin taken every other day reduced colon cancer risk. However, today’s study, which included an average of 18 years of follow-up data on about 40 000 women who were randomized to receive either aspirin every other day or a placebo, did find an effect: 47 fewer cases of colon cancer and 56 fewer cases of gastrointestinal cancer in women who took aspirin compared with the placebo group. However, the researchers did not find an overall reduction in all-cause mortality or a decrease in cancers overall in the group that took regular aspirin.
Although the aspirin itself may have reduced the risk of colon cancer, an alternate explanation may be that colon cancer was reduced among the aspirin takers because they were more likely to have colonoscopy (prompted by aspirin-related bleeding) than those who took the placebo and consequently were more likely to have polyps discovered and removed, the authors note. However, an editorial accompanying the study said this explanation seemed unlikely, given similar colonoscopy rates in the 2 groups.
The editorial author, Peter M. Rothwell, MD, PhD, of the University of Oxford, concluded that the lack of reductions in overall mortality or in overall cancer rates with long-term aspirin use “should temper any recommendations for widespread use of aspirin in healthy middle-aged women.”