A trial looking at preventing bowel cancer with aspirin or resistant starch (CAPP 2)

Cancer type:

Bowel (colorectal) cancer
Colon cancer




Phase 3

This trial looked at aspirin and starch to prevent people with a rare condition called HNPCC from developing bowel cancer.

More about this trial

People who have HNPCC (also called Lynch syndrome) have inherited a faulty gene, which increases their chances of developing certain cancers, such as bowel (colorectal) cancer.

People who have HNPCC, and their close relatives, are offered regular check ups and screening with a colonoscopy to look inside the bowel. During the test, the doctor will remove any polyps (adenomas) found in the bowel.

Resistant starch is a form of corn starch which is hard to digest. It is not broken down in the upper gut and instead finds its way to the large bowel where it is fermented by bacteria. This produces chemicals like the fatty acid butrate, which is protective against cancer. Earlier research also suggested that aspirin may prevent polyps forming.

The aim of this study was to see if aspirin, resistant starch or both can stop people with HNPCC developing bowel cancer.

Summary of results

The trial team found that aspirin reduced the number of bowel cancers developing in people with HNPCC.

937 people took part in this trial. Everybody had treatment for between 1 and 4 years.

  • One quarter had aspirin and resistant starch
  • One quarter had aspirin with ordinary corn starch (which acts as a dummy drug (placebo))
  • One quarter had dummy aspirin tablets and resistant starch
  • One quarter had dummy aspirin tablets and ordinary corn starch

Everybody had a colonoscopy before treatment started and again every 1 to 2 years after that.

Some results were published in 2008. At that time, the researchers found a similar number of people in the 4 different treatment groups had developed polyps or bowel cancer.

The planned long term results were first published in 2011 when they had followed people up for an average of more than 5 ½ years.

Of the 937 people who took part in the trial

  • 427 had taken aspirin
  • 434 had taken dummy aspirin tablets
  • 76 did not have either as they chose not to join the part of the trial looking at aspirin

The researchers looked at how many people had developed bowel cancer and found it was

  • 18 in the group who had aspirin
  • 30 in the groups who had dummy tablets

They concluded that aspirin did reduce the number of people with HNPCC developing bowel cancer. They could see this difference after people had been taking the drug for 3 to 4 years. More long term follow up published in 2012 showed no benefit in taking resistant starch.

A trial called CaPP3 started in 2014 to work out the best dose of aspirin to take and the ideal length of time people should take it for.

We have based this summary on information from the team who ran the trial. The information they sent us has been reviewed by independent specialists (peer reviewed Open a glossary item) and published in a medical journal. The figures we quote above were provided by the trial team. We have not analysed the data ourselves.

Recruitment start:

Recruitment end:

How to join a clinical trial

Please note: In order to join a trial you will need to discuss it with your doctor, unless otherwise specified.

Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Chief Investigator

Professor Sir John Burn

Supported by

Bayer Corporation
Cancer Research UK
European Union
Medical Research Council (MRC)
National Institute for Health Research (NIHR)

If you have questions about the trial please contact our cancer information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:


Please note - unless we state otherwise in the summary, you need to talk to your doctor about joining a trial.

Around 1 in 5 people take part in clinical trials

3 phases of trials

Around 1 in 5 people diagnosed with cancer in the UK take part in a clinical trial.

Last reviewed:

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