SIGGAR trial logo


The Special Interest Group in Gastrointestinal and Abdominal Radiologists (SIGGAR or SIGGAR1) trials began in 2004 and were led by Professor Wendy Atkin (Imperial College London) and Professor Steve Halligan (University College London). 

The SIGGAR study comprised two randomised controlled trials comparing three methods for diagnosing bowel cancer (also known as colorectal cancer). These methods are described in the sections below. The SIGGAR study was funded by the NIHR Health Technology Assessment (HTA) Programme.

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

The SOCCER study used data gathered during the SIGGAR trials to investigate the potential efficacy of flexible sigmoidoscopy (a technique which examines only the last [distal] part of the colon) as an alternative to whole-colon examination in patients with gastrointestinal symptoms.

Note: In July 2019, we became aware that two versions of the SIGGAR consent forms were used. The first version of the consent form did not include the option for participants to consent to the use of their data in future research. Of the 5,448 people who were randomised in SIGGAR and did not subsequently withdraw consent, we estimate that 1,890 people completed the first version of the consent form. However, the SOCCER study protocol and all supporting documents only referred to the second version of the consent form that, in addition to consenting to take part in the SIGGAR trials, also gave an option for participants to consent for their data to be used in future research. All data analysed for the SOCCER study was done in a way that no individual could be identified by the study team at the CSPRG. All results from the SOCCER study were published in such a way that no one could be identified (anonymised, aggregated tables). The North East – York Research Ethics Committee were informed and no further action was required.

Our Data Protection and Privacy Notice

Privacy notice

This privacy notice explains your rights to your personal information, what you can expect us (the Cancer Screening and Prevention Research Group) to do with your personal data and our lawful basis for doing so. This notice also explains who you should contact if you have any queries or complaints about how we are processing your personal data.

Under the 2018 General Data Protection Regulation (GDPR) and accompanying Data Protection Act (2018) ‘personal data’ is any data that can be linked to an identifiable individual (for a full definition see: Information Commissioner’s Office (ICO) website: What is Personal Data?). Some types of personal data, such as health data, are additionally classified as ‘special category personal data’. The law considers special category personal data to be more sensitive and gives it more legal protection (for more information see: ICO website: Special Category Data). As the Cancer Screening and Prevention Research Group processes (processing is the term used to refer to collecting, analysing and storing data) health data, much of the personal data we hold is considered to be special category personal data.

Who is responsible for the lawful processing of your personal data?

The GDPR and Data Protection Act define roles and responsibilities for those involved in processing personal data.

The Cancer Screening and Prevention Research Group (hereafter; CSPRG) are a research group at Imperial College London. The CSPRG can be contacted via the ‘Contact Us’ page on this website.  The data controller determines the purpose for which and the manner in which personal data is to be processed (see: ICO website: Controllers and Processors). For the personal data held by the CSPRG, the data controller is Imperial College London. The data controller’s representative for our data is the Director of Information Governance for Academic Health Sciences. All queries relating to the handling of personal data should be directed to the Imperial College London Data Protection Officer via email at  Contact details can also be found at the end of this privacy notice.

Why are we processing personal data?

The research focus of the CSPRG is gastrointestinal cancers which includes bowel cancer, also known as colorectal cancer. In the UK, every year over 41,000 people are diagnosed with bowel cancer alone and 16,000 people die from this disease. Through our research we hope to reduce the number of people being diagnosed with gastrointestinal cancer and dying from this disease. Much of our work focuses on how to help make bowel cancer screening and surveillance programmes more effective and acceptable for patients, and more efficient for the NHS, and other health services internationally. To understand the effectiveness of bowel cancer screening and surveillance programmes, we conduct large scale studies on procedures conducted and the benefits to patients.  Identifiable patient data are usually necessary to track long-term health outcomes for participants enrolled in our studies. The CSPRG therefore needs to collect and hold personal data – often special category personal data. Our more specific purposes for processing data for each of our studies are detailed on the ‘Studies’ pages of our website.

What personal data do we have?

The personal data we hold is special category personal data relating to individual health. For example, for several of our studies we analyse procedure and treatment information, information about cancers occurring, whether they progress and the patients’ long-term health outcomes. In addition, we also often require some basic information about patients such as age and gender to inform our analysis. The full details of the personal data processed for each of our studies can be found on the ‘Studies’ pages of our website.

To fulfil our research aims we obtain personal data from a variety of sources. Much of our data is either obtained directly from NHS Trusts, or via third parties such as NHS England, the Office for National Statistics, the Bowel Cancer Screening Programme, National Cancer Registries (including the Welsh Cancer Intelligence and Surveillance Unit) and Information Services Division Scotland, part of NHS National Services Scotland.  More detailed explanations of our sources of data can be found on the ‘Patient Data’ page and ‘Studies’ pages of our website.

Where data has been obtained from third party data providers under section 251 approval, national data opt-outs have been applied by the provider since 2016.

How do we process personal data?

All personal data we hold are processed in secure systems. For each active study we have completed a Data Protection Impact Assessment that has been approved by the Head of the CSPRG (as the Information Asset Owner) and the Imperial College London Data Protection Officer. No processing performed by the CSPRG involves automated decision-making or profiling. Unless stated otherwise on the ‘Studies’ pages of our website, all personal data are processed by the CSPRG and certain third parties (see ‘Third-party processing’ below).  None of our studies process or transfer individual-level personal data outside the UK.

The Imperial College Data retention schedule mandates that data is retained for ten years after the end of a study (see the College Retention Schedule here). The expected end of these ten year retention periods for each of our studies are listed under the ‘Studies’ pages of our website under the ‘How long will we retain the data?’ sections.

Third-party processing

For the purposes referred to in this privacy notice and relying on the bases for processing as set out above, we may share your personal data with certain third parties:

  • Other College employees, agents, contractors and service providers (for example, suppliers of printing and mailing services, email communication services or web services, or suppliers who help us carry out any of the activities described above). Our third-party service providers are required to enter into data processing agreements with us. We only permit them to process your personal data for specified purposes and in accordance with our policies.

What is our lawful basis for processing personal data?

Processing personal data requires justification under two legal frameworks: the GDPR/Data Protection Act 2018 and under the common law duty of confidentiality.

Article 6 of the GDPR lays out six valid bases under which personal data can be processed lawfully. We process personal data under lawful basis 6(1)(e) ‘Public task’ as: processing is necessary for the performance of a task carried out in the public interest. We are also required to have a separate lawful basis for processing the more sensitive special category personal data. Our legal basis for processing special category personal data is Article 9(2)(j) ‘processing is necessary for archiving purposes in the public interest, scientific or historical research purposes or statistical purposes […]

In addition, health data (such as that the CSPRG hold) require a separate lawful basis under the common law duty of confidentiality. In some of our studies, patients consented to be part of the study and for the CSPRG to process their data. In other studies, consent could not be sought due to practical considerations or the nature of the study. In these studies, we have obtained lawful permission to obtain and process personal data under section 251 of the National Health Act 2006. The common law legal bases for data processing in each study are explained in the ‘Studies’ pages of our website under the ‘What approvals has the study received?’ sections.

What are your rights concerning your personal data?

The GDPR grants individuals several rights concerning their personal data:

  • The right to object (to processing of the data)
  • The right to correct (inaccurate or incomplete data)
  • The right to erasure (also known as “the right to be forgotten”)
  • The right to restrict processing (e.g. while the accuracy of the data is contested)
  • The right to portability (to have a copy of any data you have provided to us)
  • The right to access (to have a copy of data we hold about you)
  • The right to withdraw consent (if you have previously consented to take part)

If you think that we might be processing your data and you wish to exercise any of the rights listed above, please get in touch using the details on the Contact Us page or by contacting the Imperial College London Data Protection Officer via email at  Though it may not always be possible for us to fulfil your request, we will respond to your query within one month.  For more information on your GDPR rights, please see guidance provided by the Information Commissioner’s Office.

Where can you direct queries or complaints?

Please be aware that individuals also have a right to complain to a supervisory authority- in this case the Information Commissioner’s Office (ICO) – if they feel their data is being used unlawfully. The ICO does recommend that you seek to resolve matters with the data controller – for our data that is Imperial College London – before contacting the Commissioner’s Office. If you wish to raise a complaint on how we have handled your personal data or if you want to find out more about how we use your data, please contact Imperial College London’s Data Protection Officer via email at, via telephone on 020 7594 3502 or via post at Data Protection Officer, Faculty Building Level 4, Imperial College London, London SW7 2AZ.

If you are not satisfied with our response or believe we are processing your personal data in a way that is not lawful you can raise your complaint with the Information Commissioner’s Office. The ICO’s address is: Information Commissioner’s Office, Wycliffe House, Water Lane, Wilmslow, Cheshire SK9 5AF; Helpline number: 0303 123 1113; ICO website:

Information relating specifically to the SIGGAR trials and SOCCER study

The Cancer Screening and Prevention Research Group (CSPRG) at Imperial College London processed special category personal data for the SIGGAR and SOCCER studies. SIGGAR and SOCCER were two closely linked projects aimed at reducing bowel cancer incidence and mortality. 

SIGGAR involved two randomised controlled trials to compare the efficacy of Computed Tomographic Colonography (CTC) to two established examination techniques: colonoscopy and barium enema to examine patients with symptoms requiring a whole-colon examination.

The SOCCER study used data gathered during the SIGGAR trials to investigate the potential efficacy of flexible sigmoidoscopy (a technique which examines only the last [distal] part of the colon) as an alternative to whole-colon examination. To fulfil the aims of the study and understand the long-term effectiveness of the different examination techniques, the CSPRG processed special category personal data to track the long-term health outcomes of study participants. The special category personal data used in this study was crucial to the success of this project, and the public good generally.

Imperial College London (the data controller for data processed by the CSPRG, see above) was the recipient of data for the SIGGAR and SOCCER studies. The special category personal data for these studies was received by the CSPRG from several sources, given below.

1. NHS Hospital trusts in England

The CSPRG received demographic information, symptom information, consent forms, trial-linked clinical notes and treatment data about patients in the SIGGAR and SOCCER studies directly from the 21 hospitals in which the SIGGAR trials were conducted. The 21 participating hospitals were:

2. NHS Digital

NHS Digital collect and process data from across the health and social care system in England. NHS Digital provided cancer and deaths data about patients enrolled in the SIGGAR and SOCCER studies to the CSPRG. NHS Digital received some of this data from the Office for National Statistics.

3. The Office for National Statistics

The Office for National Statistics process cancer and deaths data for patients in England. The Office for National Statistics provided this information to the CSPRG for the patients in the SIGGAR and SOCCER studies. The data were passed to the CSPRG via NHS Digital. 

The research team working on the SIGGAR study had access to the identifiable special category personal data for patients enrolled in the trials. The SOCCER study team had access only to pseudonymised data for the patients included in the SOCCER study. Pseudonymised data (see also GDPR Article 4.3) are personal data that can no longer be attributed to a specific individual without additional information. In this case, the SOCCER database does not contain any easily identifiable information such as names or NHS numbers.

The SIGGAR study was performed in collaboration with researchers at University College London (UCL) and the University of Birmingham. The main analysis for the SIGGAR study was done in collaboration with researchers at UCL who received subsets of the data to answer specific research questions. Researchers at UCL also received a pseudonymised subset of the data to perform a Health Psychology Assessment. Researchers at the University of Birmingham received a pseudonymised subset of the data to perform a Health Economics Analysis. Both groups received only pseudonymised data and therefore could not link the data they received to identifiers such as names and NHS numbers.

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.

The SIGGAR trials aimed to examine whether a Computed Tomographic Colonography, which you might see abbreviated as CTC or called ‘virtual colonoscopy’, could be used as an alternative to colonoscopy or barium enema. Virtual colonoscopy uses x-rays to take images of the bowel and creates 3-dimensional pictures to aid diagnosis. It does not require barium or sedation.

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 controlled 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 controlled trials, one comparing barium enema with virtual colonoscopy, and the other comparing colonoscopy with virtual colonoscopy. Once a 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.

  • Bradford Hospital, Bradford Teaching Hospitals NHS Foundation Trust, Bradford, January 2005 to December 2007
  • Frimley Park Hospital, Frimley Park Hospital NHS Foundation Trust, Surrey, December 2006 to August 2007
  • Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, December 2005 to August 2007
  • Hammersmith Hospital, Imperial College Healthcare NHS Trust, London, March 2006 to September 2007
  • St Mary’s Hospital, Imperial College Healthcare NHS Trust, London, April 2006 to August 2007
  • Leighton Hospital, Mid Cheshire Hospitals NHS Foundation Trust, Crewe, November 2005 to December 2007
  • University Hospital of North Tees, North Tees and Hartlepool NHS Foundation Trust, Stockton-on-Tees, February to October 2007
  • St Mark’s Hospital, North West London Hospitals NHS Trust, Harrow, March 2004 to November 2007
  • Nottingham City Hospital, Nottingham University Hospitals NHS Trust, Nottingham, May 2005 to September 2007
  • Nottingham Queens Medical Centre, Nottingham University Hospitals NHS Trust, Nottingham, June 2005 to October 2007
  • Oxford Radcliffe Hospital, Oxford University Hospitals NHS Trust, Oxford, December 2006 to December 2007
  • Royal Oldham Hospital, Pennine Acute Hospitals NHS Trust, Oldham, March 2005 to October 2007
  • Derriford Hospital, Plymouth Hospitals NHS Trust, Plymouth, March 2006 to November 2007
  • Queen Alexandra Hospital, Portsmouth Hospitals NHS Trust, Portsmouth, March 2005 to June 2007
  • Royal Cornwall Hospital, Royal Cornwall Hospitals NHS Trust, Truro, March 2005 to June 2007
  • Royal United Hospital, Royal United Hospital Bath NHS Trust, Bath, May 2005 to December 2007
  • Withington Hospital, University Hospital of South Manchester NHS Foundation Trust, Manchester, April 2006 to August 2007
  • Wythenshawe Hospital, University Hospital of South Manchester NHS Foundation Trust, Wythenshawe, July 2006 to June 2007
  • Queen Elizabeth Hospital, University Hospitals Birmingham NHS Foundation Trust, Birmingham, August 2004 to November 2007
  • Furness General Hospital, University Hospitals of Morecambe Bay NHS Foundation Trust, Barrow-in-Furness, September 2006 to June 2007

Who was included in the study?

During the SIGGAR trials, 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 trials.

The SIGGAR trials 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 required their de-identified data in order to ensure that the results of our findings were as generalisable as possible to all patients who needed to be investigated because they had symptoms of bowel cancer.

Data collected as part of the SIGGAR trials were also used in the SOCCER study.

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 5,448 patients who were randomised on the SIGGAR trials and did not withdraw their consent.

We hold only de-identified data for the 3,036 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 blood tests.
  • Cancer and mortality data from NHS Digital for patients in the SIGGAR trials.

Also see details on the SOCCER study.

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?

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. Data from SIGGAR was also used for the SOCCER study. SIGGAR and SOCCER were closed in February 2022, so we plan to hold the SIGGAR and SOCCER data until 2032.

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

The findings from the SIGGAR trials were published on the NHS National Institute for Health Research website and in The Lancet in 2013 for the CTC versus colonoscopy trial and the CTC versus barium enema trialImperial 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. As a result of these findings, the number of barium enema tests offered on the NHS has reduced.

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

Halligan S, Lilford RJ, Morton D, 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.