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Positive predictive value (PPV) is the chance that a positive test result is actually right: true positives divided by all positives. Because it falls as a disease becomes rarer, even a specific screening test gives mostly false alarms when prevalence is low, which is why PPV decides whether a multi-cancer blood test is useful.
Positive predictive value (PPV) is the probability that a test result saying 'cancer' is actually correct. It is true positives divided by all positives, so it depends heavily on how common the disease is in the tested population: even a highly specific screening test yields many false alarms when prevalence is low. This makes PPV central to judging Multi-cancer early detection (MCED) tests such as Galleri, and it recurs in the PATHFINDER 2 trial, the early detection roadmap, and the bottlenecks on cancers found late and on overdiagnosis and false alarms. It is also cited by Breath and volatile-organic-compound detection, Harbinger Health, and ideas on a national pathway for people with a positive multi-cancer blood test and urine DNA triage for haematuria.
Showing the technology this term belongs to: Multi-cancer early detection (MCED).
For someone offered the test, these are the numbers that describe what a result means in an NHS population: about 1 in 100 tests came back positive each year, between 46 and 58 in 100 positives were cancer, and a negative result left about 1 in 100 with an undetected cancer within the year. The test found between a quarter and a third of all cancers diagnosed in a screening round, and about half to two thirds of the 12 cancer types it was designed to find. Whether finding them this way reduces late-stage diagnoses is the primary question, and this paper says only that the answer was no; the primary-endpoint paper had not appeared on Europe PMC by 23 September 2026.
A multi-cancer blood test can be run in ordinary clinics, and most positive results can be resolved with imaging. But six in ten positives are false alarms that take months to resolve, and the test misses most cancers. Whether it reduces late-stage cancer or deaths is unknown; that requires randomised trials.
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.
Fixes the window in which a blood test could plausibly work and shows why CA 19-9 alone is not enough: half of early cases are missed even at diagnosis, and Lewis-negative patients are missed entirely.
A blood test can find early, treatable cancers in people who feel well, including cancers for which no screening exists. It is not a replacement for mammography or colonoscopy but a possible addition. Larger randomised trials are needed to show benefit outweighs harm.
Lung screening works when it uses volumetric nodule management, and it works against a no-screening control. The protocol underpins the UK Targeted Lung Health Check programme and European recommendations. Benefit in women remains less precisely estimated.
A scoring tool that needs no new test and can run in primary care records; it turns the 1 percent of Chari's cohort into a 3.6 percent group in whom imaging or a blood test becomes defensible.
The first molecular stool test to reach approval, and the template for the blood tests that followed: more sensitive for cancer, much less specific, and still poor at the precancerous lesions that screening is supposed to remove.
Shares Multi-cancer blood test as the first step for patients with non-specific symptoms, Cancerguard, CCGA: the Circulating Cell-free Genome Atlas behind the Galleri methylation test, Vanguard Study (NCI Cancer Screening Research Network).
Shares Breath and volatile-organic-compound detection, CCGA: the Circulating Cell-free Genome Atlas behind the Galleri methylation test, Vanguard Study (NCI Cancer Screening Research Network), New-onset diabetes as a signal of pancreatic cancer (and the ENDPAC score).
Shares Cancerguard, Cologuard, Multitarget stool DNA testing for colorectal-cancer screening, Multitarget stool RNA test (ColoSense).
Shares Cancerguard, Cologuard, Multitarget stool RNA test (ColoSense), Early detection roadmap: organ screening → blood tests for many cancers.
Shares Lewis-negative (Lewis antigen-negative, CA 19-9 non-secretor) status, Blood-based pancreatic cancer detection in new-onset diabetes, New-onset diabetes as a signal of pancreatic cancer (and the ENDPAC score), Run the ENDPAC score on every new diabetes diagnosis after 50 and scan the high scorers.
Shares CCGA: the Circulating Cell-free Genome Atlas behind the Galleri methylation test, PATHFINDER 2, Performance of a multi-cancer early detection test in the randomized controlled NHS-Galleri trial, NHS-Galleri.
Shares Multi-cancer blood test as the first step for patients with non-specific symptoms, PATHFINDER 2, Performance of a multi-cancer early detection test in the randomized controlled NHS-Galleri trial, NHS-Galleri.
Shares Blood-based pancreatic cancer detection in new-onset diabetes, New-onset diabetes as a signal of pancreatic cancer (and the ENDPAC score), Model to Determine Risk of Pancreatic Cancer in Patients With New-Onset Diabetes, Run the ENDPAC score on every new diabetes diagnosis after 50 and scan the high scorers.