Screening, Incidence and a New Treatment
A national bowel cancer screening programme using faecal occult blood testing is offered to people aged 50–74 every two years. Uptake is 42%. Over ten years, mortality from bowel cancer falls 16% in the screened age group, but the incidence of late-stage disease falls only 4%. Meanwhile, a new immunotherapy is approved for advanced disease; it extends median survival by 7 months but costs $120,000 per patient and causes serious immune-related adverse events in 12% of recipients. A health minister says, 'The screening programme is failing because incidence has barely changed, and the new drug is the better investment.'
1. Distinguish the outcome measures and evaluate the minister's claim that screening is failing.
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Distinguishing the measures.
- Mortality is deaths in the population; a 16% fall in the screened age group is a genuine benefit.
- Incidence of late-stage disease is the rate of new advanced cases; a 4% fall is small.
- Uptake (42%) limits how much any programme can achieve: more than half the target group is not screened.
Evaluating the claim. The minister conflates incidence with effectiveness. Screening aims to detect and remove pre-cancerous lesions and early cancers, so a successful programme may reduce mortality without a large fall in late-stage incidence within ten years, because the benefit accrues over a long latency and because low uptake dilutes effect. A 16% mortality reduction is substantial for a population programme. The correct conclusion is not 'screening fails' but 'uptake is the limiting factor'.
Alternative explanation to rule out. Falling mortality could partly reflect better treatment rather than screening; comparing screened and unscreened cohorts would separate these.
2. The minister proposes redirecting screening funds to the immunotherapy. Construct an argument comparing the two using incidence, cost and harm data.
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Case against redirecting all funds.
- Population reach: screening covers an entire age cohort; the immunotherapy treats only advanced disease. A drug that adds 7 months median survival does not prevent any cancer, whereas screening removes pre-cancerous lesions and prevents cases.
- Cost: $120,000 per patient for 7 months is a very high cost per life-year gained. The same money spent on raising uptake from 42% to, say, 60% would likely prevent more deaths across a much larger group.
- Harm: 12% serious immune-related adverse events is a significant burden that must be weighed against benefit.
Case for the drug. For patients with advanced disease, 7 months may be meaningful, and screening does not help people already diagnosed. The two are not interchangeable.
Balanced conclusion. The strongest argument is not either/or. Maintain and improve screening (targeted reminders, removing access barriers to raise uptake) while funding the immunotherapy for the narrower group who need it. Redirecting all funds would trade a broad preventive benefit for a costly, narrower treatment benefit.