Two trials looking at a new test to help diagnose older people with symptoms of bowel cancer (SIGGAR)

Cancer type:

Bowel (colorectal) cancer





These two trials compared a test called CT colonography (‘virtual colonoscopy’) with standard tests used to diagnose bowel cancer. The people taking part had symptoms that could have been due to bowel cancer.

Two of the tests that doctors use to examine the bowel and diagnose bowel cancer are colonoscopy and barium enema.

In these trials, researchers were looking at another test called CT colonography (CTC) or virtual colonoscopy.

As well as finding bowel cancer, all these tests can also show if you have non cancerous growths in your bowel called polyps Open a glossary item. Polyps can develop into cancer over a long period of time. If a polyp is found when you are having a colonoscopy, it can be removed.

It is not possible to remove a polyp during barium enema or CTC. If a polyp is seen during one of these tests, you need to have further tests. This is usually colonoscopy. Some people also need to have further tests after a colonoscopy if it was not possible to look at the whole length of their bowel.

One trial compared CTC with barium enema, the other compared CTC with colonoscopy. The main aims of the trials were to

  • See if CTC detected significantly more bowel cancers and large polyps than barium enema
  • Find out if people having CTC went on to have further tests at an unacceptably high rate compared to colonoscopy

Summary of results

The team found that a virtual colonoscopy was better at diagnosing bowel cancer and large polyps than a barium enema, and missed fewer cancers. But as it was also better at showing small polyps, people with these went on to have further tests more often than people who had a barium enema.

The trial comparing virtual colonoscopy (CTC) and barium enema analysed results from 3,804 people.

The number of people found to have a large polyp or bowel cancer was

  • 93 out of 1,277 people (more than 7%) who had CTC
  • 141 out of 2,527 people (less than 6%) who had a barium enema

CTC missed 3 out of 45 bowel cancers. Barium enema missed 12 out of 85 cancers.

In the trial comparing CTC with colonoscopy, the researchers were looking at the number of people who went on to have further tests after the first test. They have results for 1,580 people and found that the number of people who needed further tests was

  • 86 out of 1,047 people (8%) who had colonoscopy
  • 160 out of 533 people (30%) who had CTC

About a third of the further tests done after CTC may not have been necessary. They were requested because small polyps had been seen, but these are unlikely to become cancerous.

In this trial, the number of cancers found was about the same for both groups. CTC missed 1 out of 29 bowel cancers. Colonoscopy didn’t miss any.

The researchers concluded that

  • CTC was better than barium enema at finding bowel cancer or large polyps and so CTC should replace barium enema where this was possible
  • CTC was as good as colonoscopy at finding bowel cancer or large polyps – it was a safe, acceptable and similarly accurate alternative to colonoscopy, but guidelines are necessary to try and reduce the number of patients needing further tests after CTC

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 Steve Halligan
Professor Wendy Atkin

Supported by

Imperial College London
NIHR Biomedical Research Centres (BRCs) Award
NIHR Health Technology Assessment (HTA) programme
National Institute for Health Research Cancer Research Network (NCRN)
University College London (UCL)
University College London Hospitals NHS Foundation Trust

Questions about cancer? Contact our information nurses

Freephone 0808 800 4040

Last review date

CRUK internal database number:

Oracle 407

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

Alan took part in a clinical trial for bowel cancer patients

A picture of ALan

“I think it’s essential that people keep signing up to these type of trials to push research forward.”

Last reviewed:

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