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GP implications of screening for colorectal cancer

The Government wants a national programme within five years – Professor David Weller outlines the options

Colorectal cancer is the second commonest cause of cancer-related death in Western countries. Each year there are more than 30,000 new cases of colorectal cancer in the UK with an average five-year survival of 40 per cent.

Screening offers the prospect of detecting the disease at an early stage and, hopefully, bringing about improvements in survival.

There are several forms of screening that may become established in the UK over the next decade: fecal occult blood test screening and flexible sigmoidoscopy are the most likely to become part of national programmes, and both have important implications for general practice.

Fecal occult blood test

(FOBT) screening

This is the most widely evaluated form of screening for colorectal cancer in the UK. It works on the principle that cancers and polyps bleed into the lumen of the bowel, albeit intermittently, and that this blood can be detected by applying tests to stool samples.

As most GPs will be aware, there is strong evidence in support of colorectal screening using the FOBT; screening can detect cancers at an earlier stage, RCT and case-control evidence suggests removal of adenomatous polyps reduces the incidence

of colorectal cancer,

and that mortality can

be reduced by

detection of early stage tumours1,2,3.

The UK Colorectal Cancer Screening Pilot was recently completed; it examined the feasibility of screening for colorectal cancer in the UK population using the FOBT4. Invitations were sent to approximately 480,000 people via mail from dedicated screening centres in Scotland and England.

In essence, the pilot was able to demonstrate that rates of uptake in the region of 60 per cent – similar to those achieved in randomised controlled trials – are obtainable through population-based screening. While the pilot used standard guiaic-based tests that can be affected by diet and require high rates of retesting, there is interest in newer immunochemical tests which may be more reliable and feasible in population-based screening5.

Flexible sigmoidoscopy

Although flexible sigmoidoscopy can only reach the lower one-third of the large intestine, it has the advantage of direct visualisation of the mucosa and the potential to biopsy suspicious lesions. It can be conducted in primary care settings by medical and nursing staff with appropriate training.

At present a major trial examining flexible sigmoidoscopy screening is under way which will provide evidence on the potential for this modality to reduce mortality6,7 – until such evidence is available its use as a screening tool is unlikely to become widespread.

Other screening approaches

Colonoscopy and barium enema are used as screening modalities in some centres, particularly in North America8. Of these, colonoscopy is becoming the most common due to its greater accuracy, and improvements in complication rates. It is possible that other forms of screening, currently in experimental stages, will become more widespread over the next decade.

These alternative modalities include stool DNA detection and multislice CT scanning9.

Current status of screening for colorectal cancer

Randomised trials and the UK pilot of colorectal cancer screening have shown FOBT screening can reduce mortality from this disease and that this form of screening is feasible in the UK population. Nevertheless, a national programme is unlikely to be introduced immediately for a number of reasons, including cost, availability of endoscopy services, training and workforce issues.

That said, the planning process to support a screening programme for colorectal cancer has begun, and health departments in England and Scotland are working towards implementation of a programme within the next five years. This will involve consideration of a range of issues, including modalities such as flexible sigmoidoscopy and improvements in primary prevention and surgical treatments.

The GP and national screening

A national screening programme will have significant implications for general practice. The UK pilot found that, although FOBT screening was organised centrally, GPs played an important role in information provision, and managing patients whose involvement in screening had left them with unresolved issues over their health – including residual anxiety over the screening process and their likelihood of developing cancer in the future.

Hence, in common with mammography and other screening programmes, primary care will provide support to the screening process, and the workload implications of this role will be an important consideration in the implementation of a future screening programme.

References

1 Hardcastle JD et al. Randomised controlled trial of

faecal-occult-blood screening for colorectal cancer.

Lancet 1996; 348: 1472-7

2 Selby JV et al. A case-control study of screening sigmoidoscopy and mortality from colorectal cancer.

N Engl J Med. 1992; 326: 653-7

3 Towler B et al. A systematic review of the effects of screening for colorectal cancer using the faecal occult blood test, Hemoccult. Br Med J 1998; 317: 559-65

4 Weller D et al . Evaluation of the UK Colorectal Cancer Screening Pilot. A report for the UK Department of Health. Dept. Health, June 2003 www.cancerscreening.nhs.uk/colorectal/finalreport.pdf

5 Young GP et al. World Health Organisation (WHO) and World Organisation for Digestive Endoscopy (OMED). Choice of fecal occult blood tests for colorectal cancer screening: recommendations based on performance characteristics in population studies: a WHO and OMED report. Am J Gastroenterol. 2002; 97: 2499-5

6 Rhodes JM. Colorectal cancer screening in the UK: joint position statement by the British Society of

Gastroenterology, the Royal College of Physicians, and the Association of Coloproctology of Great Britain and Ireland. Gut 2000; 46: 746-748

7 Atkin WS et al. Design of a multicentre randomised trial to evaluate flexible sigmoidoscopy in colorectal cancer screening. J Med Screen. 2001; 8: 137-44

8 Kahi CJ, Rex DK. Current and future trends in colorectal cancer screening. Cancer Metastasis Rev 2004; 23: 137-44

9 Schoepf UJ et al. Multi-slice computed tomography as a screening tool for colon cancer, lung cancer and coronary artery disease. Eur Radiol. 2001; 11: 1975-85

David Weller is head of general practice, division of community health, University of Edinburgh – he led the Government evaluation of the national colorectal cancer screening pilot

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