Professor John Burns, of Newcastle University, who led the study, said he believes his team may have uncovered a simple way of controlling cancer stem cells.
The researchers gave a placebo, indigestible starch or 600mg aspirin to 1,071 patients with Lynch syndrome, a condition accounting for 5 per cent of colon cancer cases.
After five years, there have been under half as many colon cancers in the patients taking aspirin than in those on placebo (six, compared with 16).
Professor Burns commented: 'Although there were many reports that aspirin might have a beneficial effect in a range of cancers, they were from case control and epidemiological studies.
'We decided that the only way to achieve conclusive proof was to undertake a randomised trial in a high-risk population.'
Professor Burns believes aspirin may cut the chances of cancer stem cells surviving in the colon. He presented the findings at the European Cancer Organisation - European Society for Medical Oncology conference this week.
Lynch syndrome is an inherited cancer of the digestive tract, especially the colon and rectum.