The finding that a cheap drug can help in the fight against cancer is also being balanced against the fact that a daily aspirin can cause gastrointestinal bleeding, hemorrhagic strokes and other negative side effects, especially in healthy patients.
One of the studies by University of Oxford researchers looked at data on tens of thousands of men and women who participated in dozens of large, long-term randomized controlled trials. After three years, the group taking a daily aspirin, cancer risk was about 25% less than in the control group not taking aspirin. After five years, the difference was a 37% reduced risk.
The second study of five large randomized controlled studies in Britain found that daily aspirin users had a 36% reduction in the risk of metastatic cancer and a 46% decreased risk of colon, lung and prostate cancer over the control group.
The studies also showed that daily aspirin lowered the risk of cancer progressing to the metastatic stage, especially for colorectal cancer patients.
Both studies, published in the medical journal The Lancet, were led by Dr. Peter M. Rothwell, a professor of clinical neurology at the University of Oxford, who told The New York Times:
“What really jumps out at you in terms of prevention is the striking 75% reduction in esophageal cancer and a 40 to 50% reduction in colorectal cancer, which is the most common cancer right now. In terms of prevention, anyone with a family history would be sensible to take aspirin."
Experts were cautious about these results because daily aspirin increases the risk of gastrointestinal bleeding and hemorrhagic strokes. However, Dr. Rothwell's studies found that bleeding in aspirin users decreased over time and that the daily aspirin group had a lower risk of death from brain bleeds than the control group.
However, more caveats focused on the fact that the clinical trials studied were not originally meant to study cancer prevention; they were intended to examine the effects of daily aspirin on heart disease.
Two major studies that looked at the usage of low-dose aspirin to prevent cancer did not find it was linked to reductions in cancer, but Dr. Rothwell's team did not include them in their analysis because they involved use of aspirin every other day, not daily.
However, other experts said that despite the limitations of the analyses, other long-term clinical trials of aspirin and cancer are not likely to be done because such studies would be expensive and aspirin is a cheap generic drug.
Dr. Andrew T. Chan, an associate professor of medicine at Harvard Medical School and co-author of a comment published with the articles, said the studies, despite their limitations, “raise the level of excitement about using aspirin as a chemopreventive agent.”
“If you start to include the possibility that aspirin reduces the cancer risk beyond colon cancer, then the risk-benefit ratio shifts quite a bit, especially for those cancers where we have little to offer in the way of screening and early diagnosis,” Dr. Chan said.
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