A screening test can find many cancers and still fail. What matters is whether it finds cancers earlier than they would otherwise be found, and whether that changes death. Stage shift is the first test; mortality is the real one.
When a patient brings a commercial screening test, ask three questions: was it randomised, what was the primary end point, and did it change stage or death? A high detection rate, a low false-positive rate or a personal story answers none of them.
- Randomised or not?
- Primary end point: detection, stage shift or mortality?
- Was the primary end point met?
- Who funded it?
Why it matters
Detection rates sell screening tests; stage shift and mortality decide whether they help.
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