# Offer the blood test for bowel cancer only to people who refuse stool tests or colonoscopy

Source: https://onco.cc/ideas/idea-prev-blood-crc-test-for-non-responders/  
OnCo record `idea-prev-blood-crc-test-for-non-responders` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Blood tests for bowel cancer miss most precancerous polyps, so they should not replace stool tests. But for the third of people who never do any screening, a blood test may beat nothing.

## Summary

Shield (Guardant) is FDA-approved with about 83% sensitivity for colorectal cancer but around 13% for advanced adenomas; the concern is substitution away from FIT and colonoscopy. Propose a randomised trial in persistent non-responders: blood test offer versus repeat FIT offer, endpoint stage I-II cancers detected per 1,000 invited.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Offering a blood test to non-responders raises participation by at least 20 percentage points and yields more early-stage cancers per 1,000 invited than a further FIT invitation.
- Rationale: Uptake, not test accuracy, drives population benefit; a moderately sensitive test with high uptake beats an excellent test nobody takes.
- Proposed test: Run a 20,000-person RCT in a programme with good registry linkage.
- Maturity: early-clinical
- Actor: payer

## Sources

- Bottleneck evidence (The hardest cancers are found late): Crosby et al., Early detection of cancer (Science 2022): https://doi.org/10.1126/science.aay9040

## Connected records

- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [Early-onset colorectal cancer (under 50)](https://onco.cc/cancers/early-onset-colorectal/)
- fronts: [Early Detection & Screening](https://onco.cc/fronts/early-detection/)
- technologies: [Liquid biopsy (ctDNA)](https://onco.cc/technologies/liquid-biopsy/)
- drugs: [Shield](https://onco.cc/drugs/shield/)
- companies: [Freenome](https://onco.cc/companies/freenome/), [Guardant Health](https://onco.cc/companies/guardant-health/)
- bottlenecks: [Prevention we already have is not deployed](https://onco.cc/bottlenecks/b-prevention-adoption/), [The hardest cancers are found late](https://onco.cc/bottlenecks/b-early-detection/)
- key papers: [Early detection of cancer](https://onco.cc/key-papers/paper-crosby-science/)

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