Taking aspirin for several years can cut the risk of death from a wide range of cancers by between a third and half, a landmark study found.
Other evidence indicates that calcium in milk might enhance the drug's beneficial effects.
Scientists are stopping short of urging healthy people to take aspirin, which is known to increase the risk of internal bleeding. But they say the new findings shift the risk-benefit balance in favour of aspirin and could lead to a revision of medical guidelines.
Aspirin treatment to ward off cancer would probably be most effective between the ages of about 45 and 50, which is when most cancers start to develop, say the researchers.
The drug is already taken by millions of Britons at risk of heart attacks or strokes.
Regular low doses of aspirin help to prevent the changes that lead to narrowed arteries and blood clots. But in recent years, evidence has started to emerge of much wider benefits from aspirin, leading to its description as a "miracle drug".
A previous study has shown a 75-milligram dose per day can reduce death rates from bowel cancer by more than a third.
Earlier this year, scientists in the United States reported the same low dose cut the risk of men developing prostate cancer by up to 30 per cent.
The new research - the most wide-ranging to date - involved picking out cancer trends from eight studies of aspirin's effects on arteries, involving more than 25,000 patients.
Much of the cancer data had been "lost" in forgotten archives as it was not strictly relevant to the original focus of the trials. But the findings are dramatic, showing a strong association between taking aspirin and a reduced risk of dying from a host of cancers.
They include diseases affecting the stomach and bowel, oesophagus (gullet), pancreas, lungs, prostate, bladder and kidneys.
During the trials, patients were taking at least 75mg of aspirin every day for between four and eight years.
Significant benefits began to appear after five years of follow-up, with death rates for all cancers falling by 34 per cent and for stomach and bowel cancers by 54 per cent.
Study leader Professor Peter Rothwell, from Oxford University, said: "These results do not mean that all adults should immediately start taking aspirin, but they do demonstrate major new benefits that have not previously been factored into guideline recommendations."
Epidemiologist Professor Peter Elwood, from the University of Cardiff, who has conducted his own extensive studies on aspirin, said taking the drug at night and with calcium seemed to enhance its effects.
He pointed out that milk was a good source of calcium and also soothing to the stomach. "We have suggested that, in some of the new trials, we should test taking aspirin with a glass of milk," he said.
The research is published today in an online edition of The Lancet medical journal.