The study, published yesterday by researchers from Oxford University in the prestigious British journal The Lancet, aggregated the results of eight randomized clinical trials (the highest level of proof), gathering over 25,000 subjects who were followed from between 5 years and 20 years after trial inception. Subjects who had taken aspirin showed a lower risk of overall cancer death by 21%, compared to members of the control group. Risk of lung cancer death went down by 30%, esophageal cancer by 60%, colorectal cancer by 40%, prostate cancer by 10%, and gastrointestinal cancer by 35%.
The protective effect depended upon the length of daily use and upon the type of cancer. It started at 5 years for oesophageal, pancreatic, brain, and lung cancer, but needed 10 years for colorectal and stomach cancer, and 15 years for prostate cancer. The protective effect increased with duration of use. After 5 years of use, risk of death from any kind of cancer had decreased by 34%. The protective effect was shown to extend up to 20 years after trial inception, when risk of death for solid cancers was lower by 20%, and for gastrointestinal cancer by 35%. The effect was independent of dose, although most trials used low doses around 75mg -baby aspirin dose in the UK, vs 81mg in the US.
The authors of the study had already published a first article in the same journal in October, showing very significant effect for low daily doses of aspirin on the prevention of colon cancer. This additional study greatly generalizes the first one. This is the first time that prevention has been proven to work against cancer. This study, and the one that precedes it, are particularly compelling because they consist in randomized clinical trials, which are the gold standard of proof for statistical causality evaluation.
Some experts, however, caution the public not to put too much into the present study at this stage, and point out two primary limitations. The eight trials used by the study were not looking at cancer, but at heart disease and stroke prevention, and it is only through post hoc (i.e. after the fact) analysis that data processing showed the effect on cancer. There is danger in post hoc analysis because the study was not designed to specifically prove effect on cancer, and other factors may have influenced the results. “If you suddenly go back 20 years later and look at the data, it’s tempting to say the result is because of the drug,” says Dr. Derek Raghavan, chairman of the Taussig Cancer Institute at the Cleveland Clinic. to the Cleveland Plain Dealer. Another weakness of the study is that the subject sample is mostly composed of men.
Should you start taking daily doses of aspirin? Some experts advise against it at this stage, because of potential dangers resulting from aspirin use, which include hemorrhagic stroke and gastrointestinal bleeding. "Until these [further] analyses have been done, I think it's very premature to try and advise people. There's a reason statisticians say 'beware the post-hoc analysis,' "says Dr. Raghavan. "There's really no reason for people to rush off to the doctor and say 'Should I be on aspirin?'" "I definitely think we wouldn't want to make any treatment decisions based on this study," says Dr. Raymond DuBois, provost of the M.D. Anderson Cancer Center at the University of Texas.
While the authors of the study did not recommend a change in patients guidelines, the main author, Dr. Peter Rothwell, did mention that medical guidelines "may be updated on the back of these results." It is interesting to note that Dr. Rothwell, who is 46, decided to start using daily aspirin himself after seeing early study results: "It was looking as though there was something going on, and I thought it was a sufficiently large benefit to be worth doing something about." He adds:"the increased risk of bleeding is about 1 in 1,000 per year, while the decreased risk of cancer is 2,3, or 4 per 1,000 per year." Dr. Rothwell suggested that a daily aspirin regimen is "worth thinking about" if you have a family history of early cancer, that the sensible time to start would be around age 45, and that the regimen should continue for 25 to 30 years, then stop, as bleeding risk goes up very significantly around age 75. Dr. Peter Elwood of the University of Cardiff, concurs: "There's a small risk of any of us having a gastric bleed... But when you inspect the data…you find that the mortality from the bleed is not increased. In other words, aspirin seems to be increasing the less-serious bleeds." Dr. Ed Kim, lung cancer expert at the M.D. Anderson Cancer Center, says that he will "strongly consider" taking daily aspirin himself, but that he would not automatically recommend this regimen to a patient without discussing the risks along with the benefits.
What to do in front of seemingly contradictory advice? We find this study very significant. If you are middle-aged and in good health, we advise you to take the first opportunity to talk to your family doctor and discuss a daily aspirin regimen.
Want to read more about it? Try CNN, NYTimes, Associated Press, Cancer Research UK, WebMD,
CBS News, ecancermedicalscience, ACSH, Cleveland Plain Dealer, NPR, TIME, New Scientist, HealthDay/ Business Week, Discover, or the BBC.
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