The case for using aspirin to prevent cancer continues to build, particularly if people are at increased risk of the disease.
Three new studies led by researchers at Oxford University also raise the possibility that a daily low dose of the drug could be effective, not just as a preventative measure, but as an additional treatment for those with cancer.
It follows the finding that aspirin can reduce the chances of tumours spreading to other parts of the body.
The three papers by Professor Peter Rothwell of the Nuffield Department of Clinical Neurosciences and colleagues are published today, two in the medical journal The Lancet and the other in The Lancet Oncology.
Professor Rothwell says: 'We are not at the stage of recommending aspirin use in everybody, but the guidelines on use of aspirin in the healthy middle-aged population certainly need to be updated in order to take into account the effects on the risk and outcome of cancer as well as on the risk of heart attacks and strokes.'
Previous studies by this team have established that aspirin reduces the long-term risk of dying from cancer, but that these effects don’t appear until about 8-10 years after starting taking a daily low dose of the drug. The short-term effects of aspirin were less certain.
‘What we have now shown is that aspirin also has short-term effects, which are manifest after only 2-3 years,’ says Professor Rothwell.
‘In particular, we show that aspirin reduces the likelihood that cancers will spread to distant organs by about 40-50%. This is important because it is this process of spread of cancer, or “metastasis”, which most commonly kills people with cancer.’
This reduction in the risk of a cancer spreading suggests that starting taking aspirin after being diagnosed could be beneficial – assuming that the cancer has not already spread.
Professor Rothwell says: ‘No drug has been shown before to prevent distant metastasis and so these findings should focus future research on this crucial aspect of treatment of patients with cancer that hasn’t already spread.
‘We argue in our papers that new trials are still required to confirm the benefit – but that such trials should be done urgently.'
Shift in the balance of risks and benefits?
In any assessments of aspirin’s health benefits, it is important to take into account the increased risk of bleeding when taking the drug, particularly in the stomach.
The researchers report two new findings on the risk of stomach bleeds. They found that the extra risk of stomach bleeds due to aspirin falls with prolonged use – and so the risks of long-term treatment with aspirin may well be less than previously thought.
The team also showed that the risk of a fatal stomach bleed is not increased on aspirin compared with placebo. In other words, the vast majority of people make a full recovery from the stomach bleeds caused by the aspirin. The conditions that aspirin helps to prevent, on the other hand, such as cancer, stroke and heart attacks, are much more likely to be disabling or fatal, the researchers argue.
Professor Rothwell says: ‘Previous analyses of the balance of risk and benefit have simply counted the crude numbers of bleeds and other outcomes, and have not considered the time-course of these risks or the severity of the different types of events.’
Taking low doses of aspirin is known to help prevent heart disease and stroke, and for this work on cancer the Oxford researchers used data from many of the trials establishing this effect. But among people that don’t have a heart problem already, the slight benefits of aspirin are largely balanced out by the increased risk of stomach bleeds.
The new information about aspirin and cancer could begin to change the overall assessment, the researchers believe.
The benefits of daily aspirin in reducing cancer risks are larger in absolute terms than the benefits in preventing heart disease and stroke, explains Professor Rothwell, particularly with prolonged use.
Three studies set out the findings
The first Lancet paper used data for all participants in 51 randomised clinical trials comparing the effect of taking aspirin every day against no aspirin.
While these trials were interested in whether aspirin prevented vascular events such as heart attacks, they also included data on cancer deaths.
The research team found that aspirin reduced the risk of a death from cancer by 15%. This reduction in risk improved over time, reaching 37% for those on aspirin for 5 years and more.
Daily low-doses of aspirin also reduced the occurrence of cancer, not just deaths from cancer. The incidence of cancers dropped by around a quarter from 3 years and onwards, with similar reductions in men (23%) and women (25%).
The second paper in The Lancet reports on aspirin’s effect on the spread of cancer to other organs in the body, a process known as metastasis. Professor Rothwell and colleagues collected new data on cases of cancer metastasis from five large randomised trials carried out in the UK.
These trials had been conducted to investigate the use of aspirin in the prevention of heart disease. But the Oxford researchers went back to the paper records of these trials to trace information on cancers and also added data from British cancer registration and death certification systems to be able to include good information about cancer cases within the trials.
They found that aspirin reduced risk of the spread of cancer to other parts of the body by 36% over the average 6.5 year course of the studies. The effects of aspirin were independent of age and sex.
The third study, published in The Lancet Oncology, also looked at aspirin’s effect on cancer risk. This time the researchers carried out a systematic review of a different type of medical study: they looked at observational studies rather than randomised trials.
They found that the observational studies matched the randomised trial results well, showing a similar reduction in risk.
Professor Rothwell explains which types of cancer see the biggest effect: ‘In terms of preventing spread of cancer, the data suggest that the effect is largest in adenocarcinomas. These include cancers of the gut, particularly colorectal cancer, some cancers of the lung and most cancers of the breast and prostate.
‘In terms of preventing the longer-term development of new cancers, the largest reductions are seen in risk of colorectal cancer and oesophageal cancer, with smaller effects on several other common cancers.’