The Special Interest Group in Gastrointestinal and Abdominal Radiologists (SIGGAR or SIGGAR1) study began in 2004 and was led by Professor Wendy Atkin (Imperial College London) and Professor Steve Halligan (University College London). The SIGGAR trial is also known as SIGGAR1 as it was intended that there would be more trials from this organisation, which is now known as BSGAR, British Society of Gastrointestinal and Abdominal Radiologists.

The SIGGAR study comprises two randomised trials comparing three methods for diagnosing bowel cancer. These methods are described in the sections below. The SIGGAR trial was funded by the Heath Technology Assessment (HTA) Programme which funds independent research about the effectiveness, costs and broader impact of healthcare treatments and tests. It is expected that findings from the SIGGAR study will inform the national guidelines for bowel cancer diagnosis to benefit patients and the NHS by promoting the best possible care, as well as efficiency savings.

The trial is registered with the ISRCTN registry. Its unique number is 95152621.

Our Data Protection and Privacy Notice

Imperial College London is the sponsor for the studies run by the Cancer Screening and Prevention Research Group (CSPRG). We will be using special category, personal information from health care records, either directly from NHS Trusts or via third parties such as NHS Digital, the Office for National Statistics, National cancer registries, including the Welsh Cancer Intelligence and Surveillance Unit, and Information Services Division (Scotland), in order to undertake these studies where we will act as the data controller. This means that we are responsible for looking after your information and using it properly. CSPRG / Imperial College London will keep special category, personal data about you for 10 years after the study has finished.

As a University we use personal data and special categories of personal data to conduct research to improve health, care and services. As a publicly-funded organisation, we have to ensure that it is in the public interest when we use personal data and special categories of personal data from people who have agreed to take part in research or where we have section 251 approval to obtain, process and hold such data.

Your rights to access, change or move your information are limited, as we need to manage your information in specific ways in order for the research to be reliable and accurate. If you withdraw from the study, we will keep the information about you that we have already obtained. To safeguard your rights, we will use the minimum personally-identifiable information possible.

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What were the aims of the SIGGAR study?

When a person visits their doctor for symptoms that are suggestive of bowel cancer, the doctor might refer them to hospital for further investigations. Often people will be offered a test to examine the whole of the large bowel to look for abnormalities. Prior to the SIGGAR study, the tests that had proven most suitable for ‘whole colon’ examination were colonoscopy and barium enema.

Colonoscopy is a procedure during which, usually under sedation, a tube (endoscope) with a small camera attached is inserted into the rectum and guided through the large bowel to examine its surface for abnormalities. The barium enema examination involves passing a white liquid containing barium into the bowel through the rectum and then taking x-rays of the bowel.

More recently, a new imaging test for examining the bowel has been developed. This test is called Computed Tomographic Colonography, which you might see abbreviated as CTC or called ‘virtual colonoscopy’. Virtual colonoscopy uses x-rays to take images of the bowel, and creates 3-dimensional pictures to aid diagnosis. It does not require barium.

Prior to the SIGGAR study it was thought likely that virtual colonoscopy was a useful test for examining people with bowel cancer symptoms, and might have some benefits over barium enema and colonoscopy. However, the strong evidence that was needed to adopt virtual colonoscopy more widely had not been collected.

The SIGGAR study aimed to provide the robust evidence needed to support the use of virtual colonoscopy in bowel cancer diagnosis. To achieve this, we compared virtual colonoscopy with barium enema or colonoscopy in two randomised trials, to see how effective and safe virtual colonoscopy was compared with the other two tests.

What type of study was SIGGAR?

The SIGGAR study comprised two randomised trials, one comparing barium enema with the newer virtual colonoscopy, and the other comparing colonoscopy with virtual colonoscopy. During these trials, once their doctor confirmed they were eligible, a computer programme randomly assigned registered patients to receive either a ‘virtual colonoscopy’, barium enema or colonoscopy examination.

When and where did the study take place?

People were recruited to the SIGGAR trials from 21 NHS hospitals (see below) across England between March 2004 and December 2007.


Who is included in the study?

During the SIGGAR trial, there were 9,218 patients aged 55 years or over, who were referred to one of 21 participating hospitals (listed above) with symptoms of bowel cancer during the study period. Of these patients, 734 were not considered as eligible for the SIGGAR study.

The SIGGAR trial included 5,448 patients who gave their consent to be randomly assigned to receive virtual colonoscopy or barium enema (trial 1) or virtual colonoscopy or colonoscopy (trial 2). Of these, 64 patients indicated that they did not want their data to be used for the purpose of the study; therefore, these patients were excluded.

In addition 3,036 were considered as eligible for the study and registered but were not randomised as a result of either doctor or patient preference. However, we require their de-identified data in order to ensure that the results of our findings are as generalisable as possible to all patients who need to be investigated because they have symptoms of bowel cancer.

The data collected as part of the SIGGAR study are also being used in a follow-up study called SOCCER.

What type of information does the CSPRG hold for the purposes of the SIGGAR study?

The CSPRG holds personal information (such as name, full date of birth, NHS number) only for the 5,384 SIGGAR patients who were randomised on the SIGGAR trials and did not withdraw their consent (64 patients).

We hold only de-identified data for the 3036 patients who were eligible but not randomised and 734 patients who were not eligible).

Additionally, we also hold:

• clinical data including data on symptoms, endoscopy, pathology, radiology and bloods
• cancer and mortality data from NHS Digital for patients in the SIGGAR trials.

Also see details on the SOCCER study for which we are still collecting follow-up data.

What approvals has this study received?

This study was reviewed and approved by an independent ethics committee and other organisations with responsibilities for NHS patients and research involving the NHS as listed below:

  • Northern and Yorkshire Multicentre Research Ethics Committee;
  • Section 251 approval from Patient Information Advisory Group (PIAG) and the National Information Governance Board (NIGB), predecessors of the Confidentiality Advisory Group CAG);
  • Research & Development approval from the NHS Trusts managing all hospitals involved in the study.

Why do we need to hold identifiable data for this study?

The identifiable data was required during the study to collect the clinical information for consented patients. We have also used this information to collect the data required for the SOCCER study and to allow NHS Digital to identify the study participants and provide us with follow-up data on cancers/deaths.

How long will we retain the data?

This study ended in 2011. It is a requirement of Imperial College London, the organisation responsible for this study, that we hold data from all clinical trials for 10 years after the study end date. However, the data from SIGGAR is also being used for the SOCCER study which ends in November 2015, so we plan to hold this data until 2025.

What are the results of the study and what impact have they had?

The findings from the two SIGGAR trials were published on the NHS National Institute for Health Research website and in The Lancet in 2013 for both trial1 and trial2.

Imperial College London also published a news article on this in February 2013.

The SIGGAR trials were able to show that virtual colonoscopy was better than barium enema for the diagnosis of bowel cancer, and was also better value for money for the NHS. We hope that barium enema will be phased out as a result of these findings – the number of barium enema tests offered on the NHS is already reducing.

The SIGGAR trials also showed that virtual colonoscopy was generally as good as standard colonoscopy at finding bowel cancer, but had the added benefit of being a more acceptable test for many people with fewer complications.


Halligan S, Dadswell E, Wooldrage K, et al. Computed tomographic colonography compared with colonoscopy or barium enema for diagnosis of colorectal cancer in older symptomatic patients: two multicentre randomised trials with economic evaluation (the SIGGAR trials). Health Technol Assess. 2015 Jul;19(54):1-134.

Halligan S, Wooldrage K, Dadswell E, et al. Identification of Extra-colonic Pathologies by Computed Tomographic Colonography in Symptomatic Patients. Gastroenterology. 2015 Jul;149(1):89-101. 

Zhu S, Yao G, Halligan S, et al. Cost-effectiveness analysis of computed tomographic colonography versus double contrast barium enema for investigation of patients with symptoms of colorectal cancer: Economic evaluation alongside the SIGGAR trial. Value in Health. 2014 Nov;17(7): A719-A719. 

Atkin W, Dadswell E, Wooldrage K, et al. Computed tomographic colonography versus colonoscopy for investigation of patients with symptoms suggestive of colorectal cancer (SIGGAR) : a multicentre randomised trial. Lancet. 2013 Apr;381(9873):1194-202.

Halligan S, Wooldrage K, Dadswell E, et al. Computed tomographic colonography versus barium enema for diagnosis of colorectal cancer or large polyps in symptomatic patients (SIGGAR) : a multicentre randomised trial. Lancet. 2013 Apr;381(9873):1185-93.

von Wagner C, Ghanouni A, Halligan S, et al. Patient acceptability and psychologic consequences of CT colonography compared with those of colonoscopy: results from a multicenter randomized controlled trial of symptomatic patients. Radiology. 2012 Jun;263(3):723-31.

von Wagner C, Smith S, Halligan S, et al. Patient acceptability of CT colonography compared with double contrast barium enema: results from a multicentre randomised controlled trial of symptomatic patients. European Radiology. Oct 2011;21(10):2046-55.

Von Wagner R, Knight K, Halligan S, et al. Patient experiences of colonoscopy, barium enema and CT colonography: a qualitative study. Br J Radiol. 2009 Jan;82(973):13-9.

Steve Halligan, Richard J Lilford, Dion Morton, et al. Design of a multicentre randomized trial to evaluate CT colonography versus colonoscopy or barium enema for diagnosis of colonic cancer in older symptomatic patients: The SIGGAR study. Trials. 2007, 8:32