The CAPP2 ( Colorectal Adenoma/carcinoma Prevention Programme ) trial has shown a reduction in colorectal cancer incidence of over 60% in patients at genetically increased risk who use Acetylsalicylic acid ( Aspirin ) long-term.

Various observational studies have suggested Acetylsalicylic acid can lower the risk of developing cancer, but this new work is the first randomized-controlled trial to have cancer incidence as its primary end point.
The study involved 43 Centres in 16 countries and followed nearly 1,000 patients, in some cases for over 10 years. All patients were carriers of Lynch syndrome, a genetic anomaly that predisposes a person to developing colorectal cancer and a range of other solid organ cancers. At least 1 in 1000 people carry this disorder which accounts for about 1 in 30 cases of bowel cancer. People with Lynch syndrome are about 10 times more likely that the general population to develop cancer, particularly of the bowel and womb, and often at a young age.

Between 1999 and 2005 a total of 861 people began either taking two Aspirins ( 600 mg ) every day for at least two years ( 434 patients ) or a placebo ( 427 ).

The first analysis of the trial data in 2007 showed no difference in colorectal cancer incidence between those who had taken aspirin and those who had not.
However, by 2010, there had been 19 new colorectal cancers among those who had received Acetylsalicylic acid, and 34 among those on placebo, meaning those in the Acetylsalicylic acid group had an overall 44% reduced incidence of colorectal cancer.

A further analysis focused on the patients who took aspirin for at least 2 years ( some 60% of the total ), and here the effects of Acetylsalicylic acid were even more pronounced: a 63% reduced incidence of colorectal cancer was observed with 23 bowel cancers in the placebo group but only 10 in the Acetylsalicylic acid group. The effect began to be seen five years after patients starting taking the Acetylsalicylic acid.

Looking at all cancers related to Lynch syndrome, including cancer of the endometrium or womb, almost 30% of the patients taking the placebo had developed a cancer compared to around 15% of those taking Acetylsalicylic acid.

No data for adverse events were available for after the study finished; however during the intervention, adverse events did not differ between Acetylsalicylic acid and placebo groups.

According to Authors, 600 mg Aspirin per day for a mean of 25 months substantially reduced cancer incidence after 55.7 months in carriers of hereditary colorectal cancer. Further studies are needed to establish the optimum dose and duration of Aspirin treatment.

Source: The Lancet, 2011

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