Potential five-year life years associated with stage IV reductions in NHS Galleri
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Background
NHS-Galleri did not reach its prespecified primary endpoint of a reduction in combined stage III and IV cases, but reported fewer stage IV cancers after annual multi-cancer early detection screening. We estimated the potential five-year life-years associated with the cancer-specific stage IV differences observed during the two incident screening rounds.
Methods
We used intervention and control stage IV counts for ten prespecified cancers reported in the NHS-Galleri ASCO 2026 presentation. For each cancer, the randomized-arm count difference was multiplied by the difference in five-year restricted mean survival time between stage III and IV, estimated from England stage-specific five-year net survival using a constant-hazard fit. Adverse cancer-specific differences remained in the model. Results were annualized across the two incident rounds and scaled per million people screened. Sampling intervals used an independent Poisson approximation for arm-specific counts.
Findings
Across the ten evaluable cancers, the intervention and control arms had 180 and 239 stage IV diagnoses during the incident rounds. The conditional projection was 66.3 potential life-years over five years in the trial intervention cohort, equivalent to 466 per million people screened annually (95% sampling interval 190-743). For a population of 10 million, the corresponding projection was 4,664 annually (1,896-7,432). Colorectal, lung, and esophageal cancers accounted for 79% of the net projection. Pancreatic, ovarian, and lymphoid cancers contributed negatively because their observed stage IV counts favored control.
Interpretation
If the observed incident-round reduction in stage IV diagnoses represents true downstaging to stage III, it could produce meaningful population health gains. This conditional estimate is not evidence of mortality reduction. Longer follow-up remains necessary to distinguish benefit from chance, lead-time and length biases, overdiagnosis, and differences in tumor biology.
