Acetylsalicylic acid, the little white pill often sold as Aspirin, has long been more than just a pain reliever. It's already known to help prevent blood clots, strokes and heart attacks. Now, research finds it might also prevent colon cancer in those who are genetically at risk for the disease.

The first, long-term randomized controlled trial has found that regularly taking ASA, or acetylsalicylic acid, reduces the risk of developing colorectal cancer by as much as 60 per cent in patients who have an increased risk for the illness.

The study involved following nearly 900 patients in 16 countries, who were recruited between 1999 and 2005. All had Lynch Syndrome, a genetic condition that affects about 1 in 1,000 people.

People with Lynch Syndrome have a staggering 80 per cent risk of developing colorectal cancer, often in their 40s. Women with the condition are also at a high risk of developing uterine and ovarian cancer.

For the study, which appears in The Lancet, 861 people with the condition were asked to begin taking two pills every day for at least two years. Half were given pills containing 600 mg of ASA, while the other half got placebo sugar pills.

The first analysis of the patients, in 2007, showed no difference in colorectal cancer rates between those who had taken ASA and those who had not.

But by 2010, there had been 19 new colorectal cancers among those who had received ASA, and 34 among those on placebo. Those who had taken the ASA had a 44 per cent reduced incidence of colorectal cancer.

Among those who had take ASA for more than two years, they had a 63 per cent reduced incidence of colorectal cancer.

It took five years after patients started taking the ASA for the effect to be seen.

Looking at all cancers related to Lynch syndrome, including uterine and endometrial cancer, almost twice as many patients in the placebo group developed a cancer compared to the ASA group.

The study authors say the side-effects were about the same between the treated group and the placebo, though they didn't have data for side-effects from after the study period.

As for how acetylsalicylic acid might help prevent cancer, the researchers say the mechanism still isn't clear. It's possible the ASA reduces inflammation and dampens the cancer. It might have something to do with its ability to block blood vessel formation in tumours, or it could be that the ASA enhanced normal cell death, helping cells before they go cancerous.

The authors say they are now working on the next phase of the study, which will compare the effects of different doses of ASA in people with Lynch syndrome.

In the meantime, they say, "clinicians should consider aspirin prescription for all individuals judged to be at high risk of colorectal cancer, but taking appropriate measures to minimize adverse effects."

Dr. Robert Gryfe, a colorectal surgical oncologist at Mount Sinai Hospital in Toronto who specializes in patients with hereditary cancer syndromes, says that for now, this study only affects people with Lynch Syndrome, who account for only about five per cent of all colon cancer cases.

"For that group, it is absolutely an exciting finding," he told CTV News. "This is potentially exciting for the population at large; we just have to stay tuned for further results."

He added: "I wouldn't rush out and start on high-dose aspirin."

The study's lead researcher, Sir John Burn, a professor of clinical genetics at Newcastle University, in England, notes that there are risks to taking aspirin regularly.

"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," advises Burn.

He added though that for people with a strong family history of cancer, they may want to weigh the costs versus the benefits, he concludes.

With a report from CTV's medical specialist Avis Favaro and producer Elizabeth St. Philip