Positive predictive value (PPV)
Positive predictive value (PPV) is the chance that a test saying 'cancer' is right.
PPV is true positives divided by all positives, and depends on prevalence: a screening test with 99.5% specificity in a population with 1% cancer prevalence has PPV ~50-60%. Central to evaluating MCED tests like Galleri.
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.
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.
For people with a heavy smoking history, an annual low-dose CT scan is one of the few screening tests proven to reduce cancer deaths. Most abnormal scans are not cancer, so screening must be paired with careful nodule management. It does not apply to never-smokers or light smokers.
Pages like this
not linked directly; found by shared links- ProductGalleri
Shares Multi-cancer blood test as the first step for patients with non-specific symptoms, Blood-based pancreatic cancer detection in new-onset diabetes, PATHFINDER 2, A whole-population cancer interception programme: risk-stratify every adult, detect and intercept early.
- TermStage shift
Shares Breath and volatile-organic-compound detection, NELSON: volume-based CT screening reduces lung cancer deaths with fewer false alarms, A whole-population cancer interception programme: risk-stratify every adult, detect and intercept early, DETECT-A: a blood test plus PET-CT found treatable cancers in 10,000 women with no symptoms.
- TrialNHS-Galleri
Shares A whole-population cancer interception programme: risk-stratify every adult, detect and intercept early, NHS-Galleri: design of the largest randomised trial of a multi-cancer blood test, PATHFINDER: the first prospective test of a multi-cancer blood test in people without symptoms, Early detection roadmap: organ screening → blood tests for many cancers.
- TrialNLST & NELSON (low-dose CT screening)
Shares NELSON: volume-based CT screening reduces lung cancer deaths with fewer false alarms, NLST: yearly low-dose CT scans cut lung cancer deaths in heavy smokers, Overdiagnosis and false alarms, Most lethal cancers are found late.
- IdeaFAPI PET as the workup for MCED positives
Shares A 28-day national pathway for people with a positive multi-cancer blood test, A whole-population cancer interception programme: risk-stratify every adult, detect and intercept early, Multi-cancer early detection (MCED), Most lethal cancers are found late.
- IdeaLet MCED trials read out on late-stage incidence, with mortality follow-up mandated
Shares PATHFINDER 2, NHS-Galleri: design of the largest randomised trial of a multi-cancer blood test, Multi-cancer early detection (MCED), Most lethal cancers are found late.
- IdeaLung screening eligibility by risk score, not pack-years, including high-risk never-smokers
Shares NELSON: volume-based CT screening reduces lung cancer deaths with fewer false alarms, NLST: yearly low-dose CT scans cut lung cancer deaths in heavy smokers, Most lethal cancers are found late.
- ProductShield
Shares Screening, Early detection roadmap: organ screening → blood tests for many cancers, Multi-cancer early detection (MCED), Most lethal cancers are found late.