Taking a regular dose of aspirin reduces the long-term risk of cancer by around 60 per cent in people with a family history of the disease, research has revealed.
The international collaboration, including researchers at the University of Southampton and University Hospital Southampton NHS Foundation Trust, whose work is published today in The Lancet, reveals that the benefits only become obvious several years after taking the aspirin.
Evidence of the benefits of aspirin has been accumulating for over 20 years but these are the first results from a randomised controlled trial assessing the effect of aspirin on cancer.
Late last year an analysis of people who had taken part in the early aspirin trials to prevent heart attacks and strokes showed that in subsequent years they developed fewer cancers. The missing piece of the jigsaw was a randomised trial specifically looking at its effect on cancer.
The study involved Professor Diana Eccles and Gillian Crawford from the University of Southampton's Cancer Sciences Division and Wessex Clinical Genetics Service at University Hospital Southampton NHS Foundation Trust. Professor Eccles was a member of the international steering group on this ground-breaking study, while Gillian had a major involvement in recruitment and data collection across much of the central Southern area of England, including Southampton and Oxford, for the trial.
Professor Eccles says: "This landmark study provides good news for people with a genetic disposition to colon cancer because this is one of the first studies to show that aspirin can help proactively protect against development of this disease."
The study involving scientists and clinicians from 43 centres in 16 countries followed nearly 1,000 patients, in some cases for over 10 years.
The trial was overseen by Newcastle Hospitals NHS Foundation Trust and funded by the UK Medical Research Council, Cancer Research UK, the European Union and Bayer Pharma.
The study focused on people with Lynch syndrome, an inherited genetic disorder which affects genes responsible for detecting and repairing damage in the DNA. Around half of these people develop cancer, mainly in the bowel and womb. Bowel cancer is the second commonest cause of cancer death in the UK, being responsible for 16,000 deaths a year.
Between 1999 and 2005 a total 861 people began either taking two aspirins (600 mg) every day for two years or a placebo. At the end of the treatment stage in 2007 there was no difference between those who had taken aspirin and those who had not. However, the study team anticipated a longer term effect and designed the study for continued follow-up.
By 2010 there had been 19 new colorectal cancers among those who had received aspirin and 34 among those on placebo. The incidence of cancer among the group who had taken aspirin had halved - and the effect began to be seen five years after patients starting taking the aspirin.
A further analysis focused on the patients who took aspirin for at least two years and here the effects of aspirin were even more pronounced: a 63 per cent reduced incidence of colorectal cancer was observed with 23 bowel cancers in the placebo group but only 10 in the aspirin group.
Looking at all cancers related to Lynch syndrome, including cancer of the endometrium or womb, almost 30 per cent of the patients taking the placebo had developed a cancer compared to around 15 per cent of those taking the aspirin.
However, Professor Sir John Burn from Newcastle University who led the international research collaboration adds: "Before anyone begins to take aspirin on a regular basis they should consult their doctor as aspirin is known to bring with it a risk of stomach complaints including ulcers."
The international team are now preparing a large-scale follow-up trial and want to recruit 3,000 people across the world to test the effect of different doses of aspirin.