Implementation Of A National Colorectal Cancer Screening Programme: The West Experience

30.10.06

Wilson-Junger criteria for population screening
• Important health problem? YES.
• Early/latent stage? YES.
• Is natural history known? YES.
• Suitable screening test? YES.
• Agreed criteria for who should be treated? YES.
• Diagnostic and treatment facilities available? YES.
• Is programme economically viable? YES.

Is colorectal cancer important health problem? YES!

5-year survival [conditions completely curable]
• Stage 0: 100%.
• Stage I: 90%.
• Stage II: 65%.
• Stage III: 25%.
• Stage IV: 15%.

Proportion diagnosed so that can be cured [condition asymptomatic if confined to gut wall]
• Stage I: 11%.
• Stage II: 33%.
• Stage III: 33%.
• Stage IV: 23%.

If lucky, become anaemic: through investigation of anaemia, cancer becomes obvious.

Screening has two meanings
Opportunistic e.g. Europe, USA Population-based e.g. UK
Recruitment At patient-doctor consultation Systematic invitation of all eligible in population
Participation Low High
Objective Prevention of death in participants Reduction in population mortality
Total cost Low High

Performance of potential screening tests
Screening test Sensitivity Specificity
Faecal occult blood - guaiac 30-50% ~50%
Faecal occult blood - immune 54-89% >94%
Flexible sigmoidoscopy ~50% >95%
Colonoscopy ~95% >95%
CT colography 55-92% -
Faecal DNA test 41% 94%

Flexible sigmoidoscopy - MRC/CRUK "Flexisig" study
• One examination at age 55-60.
• Detects all distal adenomas.
• Detects 50% proximal adenomas.
• Recruiting closed 1999.
• Reports in 3-5 years' time.
• 4.7% normal 55-year-olds have high-risk lesions.
• In 40,000 55-year-olds, 140 cancers were found.
• ~ 55% patients with advanced proximal lesions do not have distal lesions.

CT virtual colonoscopy
>6mm >8mm >1cm
Sensitivity of virtual colonoscopy 86% 93% 92%
Sensitivity of optical colonoscopy 90% 90% 88%

DNA stool testing
• Panel of 21 mutations:
-3 x K-ras, 10 x APC, 8 x p53, Bat-26.
-Long DNA - indicative of apoptosis.
-APC and p53 most frequent mutations.
• Sensitivity for TNM I, II and III cancers 52% compared to 13% for haemoccult II.

What is screening protocol in England?
• Guaiac-based FOBT every 2 years.
• Age 60-69.
• Positive FOBT will have colonoscopy.
• Intermediate-/high-risk polyps: 3-year surveillance.
• Invitations for screening by letter.
• Patients identified by national database.
• Public education and advertising programmes.
• National quality assurance standards.

Detailed mathematical model of colorectal cancer screening constructed - each transition represented by range of probabilities.

Survival advantage: flex sig and FOBT decrease mortality - main advantage at age 70.