Taking a daily dose of aspirin lowers the chance of dying from cancer by more than a third, major research shows today.
It reveals that the pills not only reduce the likelihood of contracting the illness, they also protect against it spreading.
Oxford scientists say the evidence is so strong that in future the NHS watchdog NICE may issue guidelines telling doctors to prescribe aspirin to cancer sufferers.
In one of a series of studies involving 200,000 patients, the academics found aspirin cut the risk of dying of cancer by 37 per cent if patients took it every day for five years.
Another study found that taking aspirin for three years reduced the chance of men developing cancer by 23 per cent, and women by 25 per cent.
Researchers also found that once patients had been diagnosed with cancer, their chance of it spreading was cut by 55 per cent if they took daily doses of aspirin for at least six and a half years.
For some time scientists have known that aspirin protects against certain types of cancer, particularly those affecting the bowel and throat.
But this is the first time they have revealed it could also treat the illness by preventing tumours spreading to other organs - or 'metastasising' - which is often fatal.
Professor Peter Rothwell, whose studies are published today in the Lancet, said extra research now needed to be carried out 'urgently'.
Professor Rothwell who is based at the University of Oxford and John Radcliffe Hospital, Oxford, said: 'If NICE were to prioritise it, it would certainly be influential.
'It's certainly time to add prevention of cancer into the analysis of the balance of risk and benefits of aspirin.
'So far, all the guidelines have just been based on the prevention of strokes and heart attacks.
'This research really shows that the cancer benefit is as large, if not larger, than the benefit in terms of preventing heart attacks and strokes.
'It does change the equation quite drastically.'
Aspirin is known to reduce the effectiveness of key cells, called platelets, which cause the blood to clot.
For this reason it is prescribed to patients who have had heart attacks and strokes to reduce the chance of blood clots and try to prevent it happening again.
Scientists think that platelets are also involved in the formation of cancerous tumours.
And they believe that they spread the illness to other areas of the body.
So by making these cells less effective, aspirin helps prevent and treat cancer.
But despite this compelling evidence, Professor Rothwell urged patients not to start taking aspirin every day purely to try to prevent cancer.
Aspirin can have harmful side effects including stomach ulcers and internal bleeding in the intestines.
Other risks in adults include kidney disease and tinnitus - or ringing in the ears.
But he said that the thousands of patients currently taking aspirin to prevent heart attacks and stroke would almost certainly be also reducing their risk of dying from cancer.
Professor Peter Johnson, Cancer Research UK's chief clinician, said: 'This is an exciting development.
'It adds to the other established ways of reducing cancer risk - not smoking, keeping a healthy bodyweight and cutting down on alcohol.
'It's a good idea for people thinking of taking aspirin to discuss it with their GP, as it can sometimes have side effects such as internal bleeding especially in people over 70.
'The research also suggests that aspirin may help to prevent cancer from spreading in the body, so it could be beneficial for people already diagnosed with cancer.
'However, because of the risk of bleeding, patients should discuss this with their specialist before starting to take aspirin, and be aware of the potential for increased complications before surgery or other treatments such as chemotherapy.'
- DAILY MAIL