Can disease be detected early enough to help without causing overdiagnosis?

Evidence(5)

1. 

   FDA approves Guardant Shield for colorectal-cancer screening

   [8][9]

   26 Jul 2024

   The FDA lists Shield’s approval date as 26 July 2024. The cited FDA evidence reports colorectal-cancer detection of 83% in a 7,861-person study and false-positive results in approximately one in ten people without advanced neoplasia. The patient fact sheet also emphasizes that Shield has limited ability to detect precancerous lesions. A positive result therefore still requires diagnostic follow-up, and the approval is not evidence that population screening with Shield prevents deaths or avoids overdiagnosis.

   1

   The FDA approval established a defined colorectal-cancer screening pathway, but approval and test performance do not by themselves demonstrate reduced mortality or eliminate overdiagnosis concerns. The report treats the need for follow-up colonoscopy and limited precursor detection as central constraints on clinical and economic value.

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2. 

   NHS-Galleri primary randomized-trial results reported

   [4][5]

   3 Jun 2026

   The primary NHS-Galleri results were published online on 3 June 2026 after three years of screening in a randomized trial of 142,924 participants. The prespecified statistically significant Stage III/IV reduction endpoint was not met. Stage-IV cancers decreased by 14%, while Stage-I/II cancers increased by 16%; the NHS report likewise described fewer stage-IV diagnoses but no difference in late-stage cancers overall. These results did not demonstrate a mortality benefit, and the report notes that longer follow-up is needed to distinguish beneficial earlier detection from lead-time effects and overdiagnosis.

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3. 

   Established screening provides a benefit benchmark, with recognized harms

   [1][2]

   Date unavailable

   The NCI describes screening-detected cancers as potentially less likely to be fatal and cites substantial reductions in cervical-cancer deaths after Pap-test screening became common. It also warns that effective screening can produce overdiagnosis and overtreatment. The NCI PDQ further cautions that apparent survival improvements may reflect lead-time bias or overdiagnosis and identifies randomized controlled trials as the most definitive way to determine screening benefit. No single date for these underlying historical screening achievements is specified in the cited material.

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4. 

   PATHFINDER demonstrates feasibility but not clinical-outcome benefit

   [3]

   Date unavailable

   In the prospective PATHFINDER cohort, cancers with detectable circulating tumor DNA were more likely to be lethal than cancers with undetectable levels. The study suggested that ctDNA-based MCED might minimize overdiagnosis by preferentially detecting more lethal tumors, but it explicitly required larger trials and longer follow-up to quantify overdiagnosis. The report uses PATHFINDER as evidence of feasibility and operational burden, not as evidence of reduced mortality.

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5. 

   Modelling projects possible MCED mortality benefits

   [6]

   Date unavailable

   The cited modelling work projected potential mortality benefits for MCED screening and argued that preferential detection of more lethal cancers might reduce overdiagnosis. The model was not an observed mortality study: its estimates depended on assumptions about cancer interception, sensitivity and disease progression, with the NHS-Galleri trial identified as a source of future empirical evidence. The report therefore treats modelling as hypothesis-generating rather than conclusive.

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