Many thousands of hereditary cancers and deaths could be prevented simply by taking aspirin, a landmark study has found.
Two pills a day cut the long-term risk of bowel cancer in people with a family history of the disease by 60% and there was also evidence of a similar impact on other solid cancers with the same genetic link.
The findings, published in an online edition of The Lancet medical journal, suggest aspirin treatment could prevent up to 10,000 cancers over the next 30 years and possibly save 1,000 lives. Despite taking large doses of aspirin - two 300 milligram pills per day - patients taking part in the study suffered no undue adverse effects.
Aspirin is known to raise the risk of internal bleeding and stomach ulcers, as well as certain kinds of stroke. But according to the researchers it could be a risk worth taking for people with a high cancer susceptibility.
The study, called CAPP2, provides the most definitive evidence yet of aspirin's anti-cancer properties. It focused on patients with Lynch syndrome, a genetic fault that strongly predisposes people to bowel cancer and a number of other solid organ cancers.
Around one in 1,000 members of the general population carry the defective genes, which account for one in 30 cases of bowel cancer. Other diseases linked to Lynch syndrome include womb, ovarian, pancreatic, brain, stomach and kidney cancers.
Those affected are 10 times more likely than average to develop cancer, often at a young age. Each year around 40,000 people in the UK are diagnosed with bowel cancer and more than 16,000 die from the disease.
CAPP2 involved scientists from 43 centres in 16 countries, including the UK. Between 1999 and 2005, a total of 861 study participants identified as Lynch syndrome carriers began taking aspirin or a dummy placebo pill.
The treatment went on for two years. Initial analysis of outcomes in 2007 showed no difference in bowel cancer rates between the two groups. However, in the years that followed treatment it became clear that aspirin was having a delayed impact. By 2010 a total of 19 new bowel cancers had been identified among participants given aspirin and 34 among the placebo group. This represented a 44% reduced incidence rate associated with aspirin treatment.
Further analysis singling out the 60% of patients who took aspirin for at least two years revealed an even more striking result. Then there were just 10 cancers in the aspirin group compared with 23 in the placebo group, a difference of 63%.