British Journal of Radiology (2007) 80, 778-781
© 2007 British Institute of Radiology
doi: 10.1259/bjr/69940604
The new NHS colorectal cancer screening programme and the potential role of radiology?
V A Sahni, MBBS, FRCR
and
D Burling, MD, MRCP, FRCR
Intestinal Imaging Centre, Level 4V, St Mark's Hospital, Watford Road, Harrow, Middlesex HA1 3UJ, UK
Correspondence: D Burling, Intestinal Imaging Centre, Level 4V, St Mark's Hospital, Watford Road, Harrow, Middlesex HA1 3UJ, UK. E-mail: burling{at}doctors.org.uk
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Abstract
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The NHS Bowel Cancer Screening Programme is the first nationally coordinated screening programme to be introduced in the UK for 18 years. Currently, the screening algorithm is based upon faecal occult blood testing and colonoscopy for those screenees testing positive. This commentary provides radiologists with an update on the rationale for colorectal cancer screening, explains the organizational structure of the new UK NHS programme, and explores the possible role for radiology in the current and future screening algorithms.
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Introduction
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Following eager anticipation, the roll-out of the NHS Bowel Cancer Screening Programme has finally begun. It is the first nationally coordinated screening programme in the UK for 18 years and the first to be offered to both men and women. The purpose of this commentary is to update radiologists on the rationale for colorectal cancer screening, explain the organizational structure of the new UK NHS programme and explore a role for radiology in the current and possible future screening algorithms.
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Colorectal cancer and screening
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The case for screening is compelling: colorectal cancer is the second commonest cause of cancer-related death and yet it is largely preventable as the majority of cancers arise from within a benign precursor, the adenomatous polyp. Malignant transformation of polyps results from a well-established polyp–cancer sequence, which typically lasts a decade or more. This predictable and prolonged polyp–cancer pathway provides two possible screening strategies: prevention of cancer by detection and removal of polyps; or reduced mortality and morbidity by detection of cancer at an earlier stage. The choice of screening strategy (cancer prevention or reduction in cancer mortality/morbidity) will determine which screening test to use.
Cancer prevention
The prevalence of colonic polyps in patients over 60 years of age is high (between 30% and 50%) but not all adenomatous polyps are destined to become cancerous. The likelihood of malignant transformation is increased in a subgroup of polyps known as "advanced adenomas", so called because they are larger (maximal diameter of 10 mm or more) or contain histological dysplasia or villous components. However, this slow process of polyp growth, advancing histology and subsequent malignant transformation provides a wide window of opportunity for lesion detection. As a result, the time interval between screening tests can be lengthened, hence the 10 year interval recommended in the USA for conventional colonoscopy screening. Possible options for a preventative screening test include conventional colonoscopy and flexible sigmoidoscopy, which have both been shown to reliably detect colonic polyps.
Reduction in cancer mortality and morbidity
Even when cancer does develop, there are clear survival benefits of treating colorectal cancer at an early stage, with estimated 5-year survival rates being 95% for Dukes A (cancer confined to submucosa), 80% for Dukes B (muscular layer of wall involved but no lymph node involvement), 50% for Dukes C (lymph nodes involved) and 5% for Dukes stage D (metastatic disease). However, the progression of cancer from Dukes A to D is relatively rapid and thus the window of opportunity for detection of cancer at an early stage is considerably narrowed. As a result, the interval between screening examinations must be relatively short, hence the requirement for biennial or annual faecal occult blood testing (FOBT).
Choice of screening test for the UK NHS
Although a preventative screening strategy might appear desirable, the UK government has opted for FOBT as the primary screening test in the current algorithm. FOBT will detect only 50% of cancers (those that bleed), but the rationale is supported by randomized controlled trials showing that screening with FOBT can reduce mortality rates (by 
16% for biennial screening) — the only screening test option backed by Level 1 evidence. In addition, a large-scale pilot study (total population of 1 million) confirmed the feasibility of using FOBT with acceptable patient compliance rates (60%) and cost-effectiveness (similar to the breast screening programme).
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Organizational structure of the current screening programme
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The organizational structure will be based on a "hub and spoke" model, with five programme hubs operating a national call and recall system to send out and analyse FOBT kits, and subsequently distribute test results to all people aged 60–69 years with an opt-in clause for those aged over 70 years. Each hub will be responsible for coordinating the programme in its area and will work with up to 20 local screening centres. These centres will provide endoscopy services and specialist screening nurse clinics for people receiving an abnormal result; they will also refer patients requiring further treatment to their local hospital's multidisciplinary team [1]. At the time of writing (September 2007), there are five active screening hubs and 19 screening centres distributed across the UK .
Current screening algorithm
Approximately 2% of people who return their FOBT test kits for analysis will have an abnormal (positive) FOBT result, and they will be asked to attend a nurse-led clinic where they will be offered conventional colonoscopy. If colonoscopy is negative or a clinically insignificant polyp is found, then the individual returns to the screening population to have a repeat FOBT in 4 years. If an advanced polyp or multiple small polyps are found, then every 3 years colonoscopic surveillance is offered. If a cancer is identified, patients are referred back to their general practitioner for referral to their local hospital for treatment (which may be at a different location to the colonoscopy screening centre; see above).
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Role of radiology
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The proposed role for radiology in the current screening algorithm is limited to those screenees with an abnormal FOBT who cannot tolerate conventional colonoscopy. There has been no specific additional funding for this alternative pathway, based on experience from the pilot studies showing minimal impact on radiology resources (<3% increase in the number of barium enemas). Indeed, the pilot studies acknowledged a general decline in demand for barium enema, thus anticipating that the impact of screening on radiology may decrease further.
However, the question mark preceding "barium enema" in the algorithm provides the option for newer technologies to be utilized, and, for radiology, virtual colonoscopy (or CT colonography) holds considerable promise.
Virtual colonoscopy or barium enema?
Virtual colonoscopy is a newly established, relatively non-invasive whole-colon examination which is rapidly gaining favour amongst radiologists, allied health professionals, political figures and the general public. Evidence suggests that it is more accurate and better tolerated than barium enema, with greater potential for further improvements in performance and patient experience.
Data from published meta-analyses [2] suggest that virtual colonoscopy detects both clinically significant polyps and cancer with an accuracy similar to colonoscopy (90% sensitivity for polyps 10 mm or larger, and 96% for cancer) compared with the relatively poor accuracy of barium enema (sensitivity of 50–70% for large polyps and 85% for cancer). The screening programme targets early-stage cancers, which are generally smaller and less conspicuous, making barium enema less appealing. In addition, there is good evidence showing that patient experience is better for virtual colonoscopy than barium enema [3]: smaller rectal catheters are used; only gas is introduced per rectum; and there is less patient movement required. A general decline in interest towards barium enema, particularly amongst radiologists and trainees, suggests that this discrepancy in performance and experience may widen further. Relative safety is also highly relevant and, although the incidence of luminal perforation may be higher with virtual colonoscopy (0.03% vs 0.004% for barium enema ) [4, 5], most cases are either asymptomatic or settle with conservative management, with no reported deaths worldwide. In contrast, when perforation does occur with barium enema, it is associated with significant mortality (10–50%) due to barium peritonitis.
Finally, the focus on waiting time targets in the UK NHS favours virtual colonoscopy over barium enema, as "one stop" staging protocols enable examination of the colon with a concurrent assessment for metastatic disease. In contrast, a delay of at least 1 week is usually recommended between barium enema and staging CT to avoid barium-related artefact, thus delaying the diagnostic work-up.
Whichever colon imaging technique is used, there are currently several possible roles for radiology in the new screening programme (discussed below).
Reducing endoscopy waiting lists
Although the demand for colonoscopy is already high (a 25% increase in demand was seen over 7 years prior to 2005) [6], it is set to increase further with the implementation of the new screening programme, both for FOBT test positives and due to increased awareness amongst the general public of the need for early investigation of symptoms that are potentially attributable to colorectal cancer. However, there are widely voiced concerns that many endoscopy departments will be unable to cope with such demand, potentially leading to longer waiting lists and thwarting progress towards the UK government's 18-week target time between patient presentation and treatment. Radiology may be well positioned to offload colonoscopy waiting lists and to help endoscopy cope with the new screening workload whilst meeting the new waiting time target.
Incomplete colonoscopy
Colonoscopy is highly operator dependent and a national audit of UK practice has shown marked variability in performance, with completion rates as low as 57% [7]. In response, the new screening programme has stipulated that endoscopists must be accredited prior to performing colonoscopy for a screening centre service. However, despite this stipulation, successful colonoscopy is not guaranteed, and herein lies another potential role for radiology — incomplete colonoscopy. As only gas or barium needs to navigate through to the proximal colon (versus the "scope"), a very small percentage of radiological examinations are incomplete; exceptions include retrogradely obstructing luminal cancer or severe diverticulitis. Notwithstanding, colonic configuration and calibre have far less of an impact on technical adequacy of examinations. With this in mind, easy access to an alternative "radiological" investigation, particularly if there was the scope for same-day examination (thus avoiding the need for further bowel catharsis), might encourage colonoscopists to abandon a difficult endoscopy procedure at an earlier stage and refer to radiology.
Patient choice and co-morbidity
It is widely acknowledged that diagnostic colonoscopy is associated with a small but significant risk of complications, including death (serving as a barrier to its use as a primary screening investigation). The risk–benefit profile improves in patients who test positive to FOBT and it appears logical to offer conventional colonoscopy, with the potential of endoscopic polypectomy, to this group, particularly in the initial screening round where the incidence of larger pathology is increased.
However, approximately 50% of the FOBT-positive patients will have no significant colonic findings. This knowledge, combined with a desire to "avoid the endoscope", may reduce compliance. High compliance rates are critical for a successful screening programme, and might be acheived if FOBT-positive screenees who express dissatisfaction at the prospect of colonoscopy at the initial nurse counselling visit were offered an alternative radiological test. Our early experience at St Mark's Hospital suggests that approximately 20% of test-positive patients are failing to attend clinic to discuss further investigation (vs the 10% predicted from pilot studies). Clearly, the reasons for non-compliance are multifactorial and an in-depth discussion is beyond the scope of this commentary; however, the fear of conventional colonoscopy and possible complications may be a significant factor.
A further role for radiology may be in the examining of screenees who are deemed too frail to undergo conventional colonoscopy. Significant co-morbidity cannot be predicted prior to distribution of FOBT kits, and therefore those testing positive may be unable to tolerate the physical effects of colonoscopy, particularly the strong laxative regimen or subsequent need for sedation. Here, CT can be performed, either using a minimal preparation technique (variation on standard abdomino-pelvic CT) or virtual colonoscopy (ideally using a reduced laxative regimen). The choice of CT method will depend largely upon the degree of frailty and life expectancy; minimal preparation techniques are recommended only for cancer detection (with sensitivity of about 85% vs 96% for virtual colonoscopy).
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Virtual colonoscopy as a primary screening test?
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Given its benefits, should virtual colonoscopy be considered as a possible primary screening test instead of FOBT? In truth, there are several different competing investigations, e.g. flexible sigmoidoscopy and faecal DNA markers, each with pros and cons and a body of advocates/critics. A thorough review of these tests is beyond the scope of this commentary but the ideal test will be accurate, inexpensive, easily available and, crucially, acceptable to patients.
As mentioned above, patient acceptability translates into improved compliance, which is fundamental for a successful programme. Compliance rates of 60% were achieved in the pilot studies for FOBT but, by utilizing a biennial test, a compliant screenee will need to be tested 5 times over a 10-year period to achieve the same surveillance as a single conventional colonoscopy. It is therefore likely that compliance will decrease with repeated negative testing. As with conventional colonoscopy, virtual colonoscopy should also enable a longer interval between examinations (5–10 years). Compliance rates for virtual colonoscopy screening are currently unknown but studies showing that patients prefer virtual colonoscopy to colonoscopy or barium enema are encouraging. Moreover, research into laxative-free bowel preparation will potentially improve compliance further.
Nevertheless, the prospect of primary virtual colonoscopy screening in the UK NHS in the future would be possible only with radical increases in CT infrastructure, manpower and experience. Currently, more than a third of NHS hospitals offer virtual colonoscopy in routine clinical practice and experience is rapidly growing. However, despite initial enthusiasm, the number of examinations undertaken is very small (<20 000 examinations by 2005) compared with conventional colonoscopy, of which more than 3 million colonoscopies were performed in the UK between 1998 and 2005.
While there is growing support for virtual colonoscopy, the investment required for its use as a primary screening test is unlikely to be forthcoming, particularly given the government's understandable requirement for large multicentre, randomized controlled trial evidence of feasibility and benefits. Indeed, flexible sigmoidoscopy is a more likely alternative, with mortality data from the national "Flexiscope trial" available in the near future.
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What next?
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Given the possible roles for radiology in the current screening programme, either for reducing diagnostic colonoscopy waiting lists or as an alternative test for FOBT-positive screenees, it is important to examine whether the current level of radiology resources could respond to increased demand. Recent NHS investment has resulted in considerable expansion of multislice CT scanner capacity, providing an excellent opportunity for radiology to utilize this capacity by implementing a virtual colonoscopy service. However, successful local implementation is challenging and requires a dedicated team to produce a business plan that encompasses a shift of resources from fluoroscopy to CT, secures funding for increased radiological activity and provides sufficient expertise and staffing to offer a high-quality service. With these factors in mind, the authors consider expansion of virtual colonoscopy to be contingent upon a nationally coordinated programme of training and accreditation (akin to national training centres for colonoscopy), with validated courses offered by centres with high patient throughput enabling "hands on" experience of virtual colonoscopy techniques and practical advice on service implementation.
Radiographer teams with prior experience of barium enema and/or acquisition of standard abdomino-pelvic CT, supported by enthusiastic radiologists, are likely to be the most pragmatic and cost-effective solution for delivering a service with sufficient patient throughput. The potential benefits of computer-aided diagnosis and development of laxative-free bowel preparation to improve reader accuracy, optimize workflow and enhance patient experience are also likely to enhance the future role of virtual colonoscopy.
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Summary
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The new colorectal cancer screening programme offers considerable opportunity for radiology to work alongside endoscopy departments to deliver high-quality, time-efficient complementary investigations to the benefit of patients. We consider that radiology is fundamental to the success of this programme and the role of radiology should be promoted and recognized. We believe a shift from barium enema to virtual colonoscopy is desirable but this will require a nationally coordinated programme to support radiology teams in this endeavour.
D Burling provides remunerated consultant advice for Medicsight plc, London, and Barco plc, Edinburgh, virtual colonoscopy software development companies. Neither author received any funding for this article.
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Acknowledgments
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The authors would like to thank Dr Stuart Taylor and Mr Omar Faiz for their help in preparing this manuscript.
Received for publication March 14, 2007.
Revision received May 14, 2007.
Accepted for publication May 23, 2007.
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References
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- NHS Bowel Cancer Screening Programme website. Available from: http://www.cancerscreening.nhs.uk/bowel/index.html [accessed 2 February 2007]
- Halligan S, Altman DG, Taylor SA, Mallett S, Deeks JJ, Bartram CI, et al. CT colonography in the detection of colorectal polyps and cancer: systematic review, meta-analysis, and proposed minimum data set for study level reporting. Radiology 2005;237:893–904.[Abstract/Free Full Text]
- Taylor SA, Halligan S, Saunders BP, Bassett P, Vance M, Bartram CI. Acceptance by patients of multidetector CT colonography compared with barium enema examinations, flexible sigmoidoscopy, and colonoscopy. Am J Roentgenol 2003;181:913–21.[Abstract/Free Full Text]
- Burling D, Halligan S, Slater A, Noakes MJ, Taylor SA. Potentially serious adverse events at CT colonography in symptomatic patients: national survey of the United Kingdom. Radiology 2006;239:464–71.[Abstract/Free Full Text]
- Blakeborough A, Sheridan MB, Chapman AH. Complications of barium enema examinations: a survey of UK Consultant Radiologists 1992 to 1994. Clin Radiol 1997;52:142–8.[CrossRef][Medline]
- Hospital Episode Statistic database. Available from: http://www.dh.gov.uk/PublicationsAndStatistics/Statistics/HospitalEpisodeStatistics/fs/en [accessed 2 February 2007]
- Bowles CJ, Leicester R, Romaya C, Swarbrick E, Williams CB, Epstein O. A prospective study of colonoscopy practice in the UK today: are we adequately prepared for national colorectal cancer screening tomorrow? Gut 2004;53:277–83.[Abstract/Free Full Text]
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Abstract
Introduction
