A British study has found that regular intake of aspirin could cut inherited colorectal cancer risk by 60 percent.
The trial -- considered to be broad in sample and long in duration -- confirms evidence elsewhere that aspirin has a protective effect against cancer of the colon and rectum, it said.
The study enrolled patients with Lynch Syndrome, a fault in genes charged with cellular repair that leads to colorectal and other cancers.
Lynch Syndrome occurs in around one in 1,000 people and accounts for about one in 30 cases of bowel cancer, The Lancet said.
A total of 861 patients were randomly designated to take either two aspirins daily, for a dose of 600 mg, or a harmless dummy pill, known as a placebo, for at least two years. They were then regularly given colon exams.
When the data from this study were first examined in 2007, there was no difference in colorectal cancer incidence between the groups.
But things changed when the researchers checked again a few years later.
By this time, there had been 34 cases of colorectal cancer in the placebo group but 19 in the aspirin group -- a reduction in incidence of 44 percent.
The doctors then looked further at those patients (60 percent of the total) who had been taking the aspirin or the placebo beyond the two-year minimum.
In this sub-group, the figures were even more impressive.
There were 23 cancers in the placebo group, but only 10 in the aspirin group, amounting to a fall of 63 percent. The difference began to be seen after five years.
In the light of this discovery, further research has been launched to see what is the best dosage and duration of aspirin treatment.
"In the meantime, clinicians should consider aspirin prescription for all individuals judged to be at high risk of colorectal cancer, but taking appropriate measures to minimise adverse effects," says the paper, headed by John Burn, a professor of clinical genetics at Newcastle University, northeastern England.
Last year, a study also published in The Lancet, found that rates of cancer of the colon, prostate, lung, brain and throat were all reduced by daily aspirin use. For the colon, the risk over 20 years declined by 40 percent.
Many doctors recommend regular use of aspirin to lower the risk of heart attack, clot-related strokes and other blood flow problems. A downside of extended daily use is the risk of stomach problems.