Does daily aspirin reduce the risk of developing or dying of certain cancers? Although some new studies add to the evidence base that aspirin may have such benefits, some caution that more data are needed to weigh risks of treatment and determine which patients might benefit.
A pooled analysis of individual patient data, published online in the Lancet in 2010, suggested that daily aspirin reduced death due to cancer among 25 570 patients enrolled in 8 analyzed trials by 21% (327 deaths among 14 035 taking aspirin vs 347 deaths among 11 535 control participants). In February of this year, the Archives of Internal Medicine published a meta-analysis of 9 trials involving more than 100 000 participants suggesting that aspirin did not reduce cancer mortality. But yesterday, 2 studies published in the Lancet and another in Lancet Oncology suggest, once again, that daily aspirin use reduces cancer mortality.
In one of the Lancet studies published yesterday, involving analysis of 34 trials with 69 224 participants, researchers found that aspirin use reduced the risk of cancer death by 15% (562 vs 664 deaths). The second study, which looked at the effect of aspirin on cancer metastasis among 987 individuals who developed a new solid cancer diagnosis while enrolled in 5 aspirin trials, found that after 6.5 years, aspirin use reduced the risk of cancer with distant metastasis by 36% (92 definite distant metastasis per 60 656 person-years for those taking aspirin vs 118 definite distant metastasis per 47 830 person-years for control participants). The Lancet Oncology observational study found aspirin use associated with a 38% risk reduction in developing colorectal cancer (1551 cases of colorectal cancer occurring among 12 659 individuals who took aspirin compared with 2664 cases of colorectal cancer occurring among 18 153 individuals who did not take aspirin).
But there are still many unresolved questions about aspirin’s potential benefits in reducing cancer risks, said Kausik Ray, MBChB, MD, a coauthor of the Archives study and a professor at St George’s University of London in England, in an interview via e-mail. Ray noted that these new studies did not include analysis of 2 of the largest randomized trials in primary prevention—the Women’s Health Study and the Physicians’ Health Study—which found no association between aspirin use and a reduction in cancer incidence or death. “The data do not tell us about who to treat with regard to risk and benefit; you need to treat about 1890 people for 1 year to prevent 1 new cancer. In contrast, for every 1095 people treated for 1 year, there is 1 extra major noncerebral bleed,” he noted. “So on average, there are about 2 extra bleeds per incident cancer prevented.”
Ray advises waiting for results from ongoing rigorous trials before embracing the hypothesis that aspirin use reduces cancer-related risks. “These studies published add considerably to our understanding, but guidelines should not change on the basis of these for general populations; we need the results of ongoing studies which accurately record cancer incidence and document nontrivial bleeds over extended follow-up to determine net benefit,” he said. “Beyond that, we need to determine who is at high absolute risk of bleeding and who is at high absolute risk of cancer to determine on a personalized level whether the treatment is suitable.”