What is the accuracy of the Galleri (multi-cancer early detection) blood test?

Accuracy of the Galleri Cancer Detection Blood Test

The Galleri multi-cancer early detection (MCED) blood test shows promising preliminary results with high specificity, but its clinical utility for population-wide screening remains unproven as large-scale validation studies are still ongoing.

Current Evidence on Galleri Test Performance

The Galleri test is a blood-based screening tool designed to detect multiple types of cancer at early stages by analyzing cell-free DNA (cfDNA) in the bloodstream. Current evidence suggests:

• The test aims to detect up to 50 different cancer types at potentially curable stages 1
• Preliminary findings indicate high specificity (low false-positive rate) 2
• The test is currently being evaluated in a large-scale NHS-Galleri trial in the UK, involving over 140,000 participants aged 50-77 years 3
• The NHS trial is designed to determine whether the MCED test can reduce late-stage cancer incidence when used in asymptomatic screening 3

Limitations and Concerns

Several important limitations exist regarding the Galleri test:

• Complete validation data on test sensitivity (ability to detect actual cancers) across all cancer types is still pending 1
• Scientists have expressed concerns about the sensitivity and specificity claims 1, 4
• The test has not yet completed the rigorous validation process that established screening tests have undergone 2
• No randomized controlled trials with mortality outcomes have been completed 2

Context Within Cancer Screening Principles

When evaluating any cancer screening test, several key principles should be considered:

• A screening test must be able to detect the majority of prevalent or incident cancers at the time of testing 5
• The benefits of testing must outweigh the risks, including false positives that may lead to unnecessary procedures 5
• The cost of testing should be reasonable compared to expected benefits 5
• Testing must be practical and feasible for widespread implementation 5

Psychological Impact Considerations

The psychological impact of receiving a cancer signal from the Galleri test is being studied:

• The sIG(n)al study is evaluating anxiety levels and psychological consequences in individuals who receive a positive result 6
• This research recognizes that any screening method requires careful consideration of potential psychological harms 6

Current Status and Recommendations

The Galleri test represents an emerging approach to cancer screening but:

• It is still considered investigational and not yet recommended for routine clinical use
• The NHS-Galleri trial will help determine its clinical utility for population screening 3
• Results from this trial will provide clearer understanding of the test's efficacy within healthcare systems 1

Comparison to Established Screening Methods

Unlike established screening methods such as colonoscopy or mammography:

• The Galleri test has not yet demonstrated reduction in cancer mortality
• Traditional screening tests have undergone decades of validation and refinement 5
• Established screening methods have proven efficacy in reducing both cancer incidence and mortality for specific cancer types 5

While the Galleri test shows promise as a multi-cancer screening tool, patients and providers should understand that it remains in the validation phase and should not replace established, evidence-based cancer screening methods. The results of ongoing large-scale trials will be crucial in determining its ultimate role in cancer detection and prevention.