Reading time: 4 – 6 minutes
It is old news that aspirin is good for your heart. But a recent report published in The Lancet, the premiere medical journal in the United Kingdom, claims that at least 75mg of aspirin every day can also reduce the risk of developing many different types of cancers.
There is already evidence that taking aspirin every day for five years can reduce the risk of colorectal cancer. Moreover, aspirin has been shown to reduce the incidence and/or growth rate of a number of cancers in animal models. To determine if aspirin can reduce the risk of other cancers in humans, Peter Rothwell and colleagues at the University of Oxford undertook a meta-analysis of eight randomized trials originally performed to study aspirin’s role in preventing vascular events. This study was independent of any commercial interests.
The researchers included eight clinical trials, comprising 25,570 people, that compared daily aspirin to placebo for a mean of four years. Five year follow-up data were available on individual patients from seven of the trials and twenty year follow up data were available for three of those. At both follow-up time points aspirin reduced the risk of cancer by about 20%. Aspirin reduced death from gastrointestinal cancers and non-gastrointestinal solid cancers like those of the lung, prostate, bladder and kidney, but not from hematological cancers. This may be because aspirin seemed to only reduce deaths from cancers that are predominantly adenocarcinomas, meaning that they originated from epithelial cells — cells that line the cavities and organs in the body and thus form the boundary between one tissue and another. Aspirin had no effect on other, non-cancer deaths.
The benefits of taking aspirin were observed primarily after five years. In patients followed for twenty years, the longer they took aspirin the more their risk decreased. However, as long as they were taking at least 75mg, larger doses of aspirin did not confer a larger benefit.
The authors took great pains to ensure that their findings were not sullied by any kind of bias. In their favor, although cancer deaths were recorded during and after the trials they analyzed, these trials were not initially performed to study cancer. They do note that since study participants were subject to more thorough medical scrutiny than the general public, perhaps their cancers might have been diagnosed earlier and this might account for lower death rates. However this did not seem to be the case for colorectal cancer, which was already known to be reduced by aspirin. Moreover, some of the cancers they examined – notably, esophageal cancer – have such low cure rates that early detection wouldn’t really matter. Unfortunately, there were too few women enrolled in the three trials with long term follow up data for them to evaluate aspirin’s effects on breast cancer and gynecological cancers. In the future they plan to extend their analysis to beyond twenty years to look for any late rebound in cancer deaths, and to see if they can replicate their findings with alternate-day — instead of daily — aspirin.
Much money, time, and effort has been spent in finding drugs to treat cancer, but less has been done on identifying and using drugs to prevent cancer. Aspirin is readily available, easy to store and has minimal side effects for most healthy adults. Dr. Rothwell has data demonstrating that other antiplatelet drugs do not reduce the risk of dying from cancer, so he suggests that people who require antiplatelet treatment should certainly be taking aspirin rather than another option. And since people in the developing world face a 40% chance of developing some form of cancer over the course of our lifetime, an aspirin a day might not be such a bad idea.
- Rothwell et al. Effect of daily aspirin on long-term risk of death due to cancer: analysis of individual patient data from randomised trials. Lancet. 2011 Jan 1;377(9759):31-41. Epub 2010 Dec 6.