# A mandatory decision aid before any multi-cancer blood test

Source: https://onco.cc/ideas/idea-prev-mced-pretest-decision-aid/  
OnCo record `idea-prev-mced-pretest-decision-aid` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

People are told a blood test can find fifty cancers, but not how many false alarms or how much is unknown. A short, tested decision aid before the test would make consent real.

## Summary

People are told a blood test can find fifty cancers but not how many false alarms or how much is unknown, so this idea requires a standardised, regulator-approved decision aid before any multi-cancer blood test. The aid would quantify false positives, unresolved positives, overdiagnosis uncertainty and the absence of outcome evidence, since consumer marketing of MCEDs has run ahead of trials. Decision aids improve knowledge and reduce overuse in PSA screening, and MCEDs carry greater uncertainty. A 2,000-person RCT in a screening-age population would measure informed choice and uptake. Speculative in maturity, it addresses the bottlenecks Overdiagnosis and false alarms, Patients lack understanding, navigation and agency, and Misinformation and unproven therapies.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: The decision aid improves knowledge scores by at least 20 points and reduces uptake among low-risk individuals without reducing uptake among high-risk individuals.
- Rationale: Decision aids improve knowledge and reduce overuse in PSA screening; MCEDs carry greater uncertainty.
- Proposed test: Run a 2,000-person RCT in a screening-age population.
- Maturity: speculative
- Actor: regulator

## Sources

- Bottleneck evidence (Overdiagnosis and false alarms): Welch & Black, Overdiagnosis in cancer (JNCI 2010): https://doi.org/10.1093/jnci/djq099

## Connected records

- fronts: [Early Detection & Screening](https://onco.cc/fronts/early-detection/)
- technologies: [Multi-cancer early detection (MCED)](https://onco.cc/technologies/mced/)
- bottlenecks: [Misinformation and unproven therapies](https://onco.cc/bottlenecks/b-misinformation/), [Overdiagnosis and false alarms](https://onco.cc/bottlenecks/b-overdiagnosis/), [Patients lack understanding, navigation and agency](https://onco.cc/bottlenecks/b-patient-voice/)
- key papers: [Overdiagnosis in cancer](https://onco.cc/key-papers/paper-welch-j-natl-cancer-inst/), [PATHFINDER: the first prospective test of a multi-cancer blood test in people without symptoms](https://onco.cc/key-papers/paper-pathfinder-lancet-2023/)

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