Aspirin was hailed as a wonder-drug in the 1800s when it was first purified – the first anti-inflammatory medication that did not have the severe side effects of steroids.  More recently aspirin’s benefits in stroke and heart attack prevention have been proven.  This week another possible benefit of aspirin has been uncovered.

An important study published in The Lancet attempted to find any effect of aspirin on cancer prevention.  I’ve written frequently about the myriad substances that are falsely claimed to prevent cancer after an observational trial shows that people who take X get cancer less frequently then people who don’t take X.  These studies are all meaningless since the only way to test the effects of X is to randomize some patients to take X and others to take placebo.  That’s what’s so tantalizing about this week’s study – it’s a review of randomized trials.

The investigators reviewed all randomized trials which randomized patients to aspirin versus placebo for at least four years.  These studies happened back in the 1970s and 80s and were designed to test aspirin’s ability to prevent strokes and heart attacks.  The investigators looked at individual patient data from this handful of studies and extracted information about cancer deaths.  They counted the number of patients who died of various cancers in the aspirin group and the control group.  The results were impressive.

During the trials themselves, the patients in the aspirin group had significantly fewer deaths due to cancer than the placebo group.  For every about 150 patients who took aspirin rather than placebo for several years, one cancer death was prevented.  This effect was large enough that the mortality from all causes was smaller in the aspirin group.  For every approximately 110 patients who took aspirin, one death from any cause was prevented.  Interestingly the benefit only became apparent 5 years after randomization.  This time delay suggests that that the effect of aspirin is not on cancers that are already present but that aspirin either prevents cells from becoming cancerous or kills very small numbers of malignant cells.

The investigators then followed up on cancer deaths in these patients in the subsequent decades since the end of the trials.  These results were even more striking.  The benefit of aspirin in preventing death from cancer persisted over time even though many of the patients discontinued aspirin back in the 80s when the trials stopped.  There were some consistent patterns across the data.  The benefit of aspirin for cancer mortality prevention was present in each of the trials and was greater with the trial duration.  That is, the longer that people took aspirin rather than placebo, the greater reduction in cancer death risk.  Death from esophageal, stomach and colorectal cancer were most affected.  Deaths from other cancers however, such as leukemias, were not decreased.  Also, interestingly, the benefit was independent of the dose of aspirin, suggesting that a “baby” dose of 81 mg daily is sufficient.

So should we all start taking daily aspirin?  Should we just put it in the water supply?

Not yet.

First of all, children should not take aspirin because of the risk of Reye’s syndrome.  Second, the trials reviewed in this study involved almost exclusively men, so we have no idea if the results can be generalized to women.  (And, importantly, we don’t know the effects of aspirin on cancers that affect women exclusively – breast, ovarian, and uterine cancer.)

Aspirin also has some risks, the most serious being intestinal bleeding and hemorrhagic stroke (bleeding in the brain).  But numerically, these risks seem to be much smaller in magnitude than the benefit of cancer mortality prevention.  Prior to this study these risks had to be balanced against the benefits of aspirin in preventing strokes and heart attacks.  In people with no risk factors for stroke or heart attack the risks outweighed the benefits.

But now, at least for adult men, the idea of daily low dose aspirin for cancer prevention seems compelling.  Lots of experts in the media are cautioning that more information is needed, but what better information could we hope for?  This study is using 20 years of follow up.  Better information will take decades more.

I’m not making any recommendations as of now, and obviously each of you should discuss this with your doctor.  I’m going to discuss this paper with trusted colleagues over the next weeks.  My initial hunch is that we may have reached the tipping point in favor of daily aspirin in adult men.

Learn more:

New York Times article:  Aspirin Helps in Reducing Cancer Deaths, a Study Finds

Los Angeles Times article:  Baby aspirin linked to reduced cancer deaths

The Lancet article:  Effect of daily aspirin on long-term risk of death due to cancer: analysis of individual patient data from randomised trials