Ethical issues and

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• Ethical issues and
• cancer screening

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Efficacy

• The extent to which a specific intervention,
  procedure, regimen, or service produces a
  beneficial result under ideal conditions.
  Ideally the determination of efficacy is based on
  the results of a randomised controlled trial.
• Last JM (ed). A Dictionary of Epidemiology.
  Third edition New York Oxford University Press,
  1995.

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Effectiveness

• The extent to which a specific intervention,
  procedure, regimen, or service, when deployed in
  the field in routine circumstances, does what it
  is intended to do for a specified population.
• Last JM (ed). A Dictionary of Epidemiology.
  Third edition New York Oxford University Press,
  1995.

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Assessing the Efficacy of Screening

• Lead-time bias
• Length bias
• Selection bias
• Overdiagnosis bias

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• Screened
• X X
  death
• Not screened
• X X
  death
• Disease begins Screen diagnosis Signs/symptom
  s

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• Screened
• X X
  death
• Not screened
• X X
  death
• Disease begins Screen diagnosis Signs/symptom
  s
• Survival time

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• Horizontal lines represent the pre-symptomatic
  screen-detectable phase in various individuals

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screen screen

• __________ ____________________________
• _______________ __________ ___________
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Cumulative breast cancer mortality

• (Deaths per 1,000 women entered after 7 years
  follow-up)
• Trial Non-attenders Controls
• HIP 2.7 4.3
• Stockholm 1.8 1.5
• S2C 4.5 2.1
• Malmo 5.6 3.1

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Design of RCT

• Study participants
• Intervention group Control group
• Outcome
• (breast cancer mortality)

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Randomised controlled trial

• Population-based
• Appropriate outcome measure
• Intention to treat analysis

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• Population based screening differs from other
  medical interventions because it is offered to
  asymptomatic people with the understanding that
  they will benefit

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Benefits and risks of screening for cancer

• Benefits Risks
• Improved prognosis for some Longer morbidity
  for those
• people diagnosed by screening. whose prognosis
  is unaltered.
• Less radical treatment which Over-treatment of
  questionable
• cures some people with early cancer. abnormalities
  .
• Reassurance for those with False reassurance for
  those with
• negative test results. false negative results.
• Anxiety and sometimes morbidity for
  people with false positive results.
• Adapted from Chamberlain JM. J Epid Com Hlth
  1984 38 270-7.

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Sensitivity and Specificity of FOBT

• Nottingham RCT
• Sensitivity 53.6
• Specificity 98
• PPV 10
• Hardcastle JD, Chamberlain JO, Robinson MHE, et
  al. Randomised controlled trial of faecal-occult
  blood screening for colorectal cancer. Lancet
  1996 348 1472-7.

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Predicted outcome of 1,000 FOBTs

• True positives 2
• False negatives 2
• False positives 18
• True negatives 978
• Number requiring colonoscopy 20
• Number diagnosed with CRC 2
• Number diagnosed with an adenoma gt 10mm 6
• Number with no abnormality detected 12

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