NHS-Galleri: design of the largest randomised trial of a multi-cancer blood test
The NHS-Galleri design paper is the protocol for a 140,000-person randomised trial in England testing whether three annual Galleri blood tests reduce late-stage (III-IV) cancer diagnoses, the first MCED trial powered for a stage-shift endpoint.
NHS-Galleri (ISRCTN91431511) enrolled about 140,000 asymptomatic adults aged 50-77 through NHS England, randomised 1:1 to annual Galleri testing for three years with results returned, or to blood draws stored without testing. The design paper set out the primary endpoint of a reduction in stage III-IV cancer incidence between arms, with secondary endpoints including stage IV incidence, cancer-specific mortality and test performance.
The trial deliberately over-sampled deprived and ethnically diverse communities using mobile clinics. Results were reported in 2026; the trial record in this corpus tracks the primary and secondary outcomes and the regulatory response.
The design is important in its own right: it established stage shift as a pragmatic proxy endpoint for screening trials of multi-cancer tests, a choice that remains contested.
- About 140,000 participants randomised, recruited through mobile clinics across NHS regions in England
- Primary endpoint: absolute reduction in stage III-IV cancers in the intervention arm; key secondary endpoint: stage IV incidence
- Test results were not returned in the control arm, preserving blinding of the population and clinicians
- Population enriched for deprived and minority communities, unusual for a screening trial
NHS-Galleri is the trial that will decide whether a blood test for many cancers at once should be offered by a health system. Its endpoint is a reduction in late-stage cancer rather than deaths, so even a positive result leaves the mortality question to be settled by longer follow-up.
- Stage shift is a surrogate: fewer late-stage cancers does not guarantee fewer deaths, and lead-time and overdiagnosis can distort it
- Three annual rounds is short for detecting slow-growing cancers
- A single commercial test; results may not generalise to other MCED assays
- Sponsor involvement in design and analysis (GRAIL) was substantial