Polyps and Bowel Cancer Screening

SR Brown, Sheffield Teaching Hospitals

Randomised controlled trials have demonstrated that colorectal cancer mortality can be reduced by screening using the faecal occult blood test (FOBt) (1) In the light of this a two pilot studies were established in the UK in 2000 to examine the feasibility of population based screening for
colorectal cancer. An evaluation of the first (prevalent) round was undertaken in 2003 at the 2 pilot sites (2). A subsequent incident round evaluation was completed in 2006 (3).

The success of the pilot studies has led to the gradual roll out of the bowel cancer screening programme throughout the UK. This is currently ongoing.

The essential concept behind the recommended screening programme is for all patients between 50 and 69 to be offered FOB testing every 2 years. Weakly positive tests will be offered rescreening with dietary restrictions. Strongly positive tests and those with consistent weakly positive tests will be offered a colonoscopy by a dedicated screening service.

Overall about 2% of all those undergoing FOBT will be considered as positive and go onto colonoscopic testing. For these positive result patients the incidence of neoplasia is very high. Approximately 47% of those with a positive FOB who undergo colonoscopy in the prevalent round will have neoplasia and about 12% will have cancer. This may fall off slightly (to approximately 40% and 7% respectively) in the incident round. Analysis of the pilot study prevalent and incident rounds indicate the likelihood of neoplasia increases with age, male sex and deprivation. Of the cancers about 16% will be polyp cancers potentially treatable endoscopically.

The high incidence of neoplasia and the potential for such neoplasia to require complex and meticulous endoscopic therapy for adequate treatment has implications for those carrying out the screening lists. The most specific implications include;

1. A positive FOBt result for the patient results in anxiety and therefore waiting times for colonoscopy must be low.
2. Screening endoscopy lists must be limited in size as each individual colonoscopy may have a prolonged therapeutic time.
3. The high polyp detection rate means that there will be a subsequent increased workload due to the required polyp surveillance. Surveillance interval requires further research. Current recommendations may be too cautious.
4. Perhaps most importantly a robust assessment and quality assurance programme is required to ensure only endoscopists of adequate calibre and endoscopic skill are allowed to carry out the colonoscopic screening. Such a programme is difficult to implement given the nature of colonoscopy. However, as competence in colonoscopy should be a parameter for all independent practitioners, it is quite possible such an assessment will eventually be rolled out for all rather than just those carrying out screening.

References
1. Towler B, Irwig L, Glasziou P, Kewenter J, Weller D, Silagy C. A systematic review of the effects of screening for colorectal cancer using the faecal occult blood test, Hemoccult. BMJ 1998;317:559.
2. UK Colorectal Cancer Screening Pilot Team. Evaluation of the UK Colorectal Cancer Screening Pilot. Final report. http://www.cancerscreening.nhs.uk/bowel/pilotevaluation.html . 2003.
3. English Pilot of Bowel Cancer Screening: An evaluation of the second round.

Final Report to the Department of Health. http://cancerscreening.org.uk/bowel/pilot-2nd-round-evaluation.html 2006.