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Ep 39 – Early detection of cancer in primary care: what role for the Galleri test?


Posted 8 Mar 2022

Dr Kevin Fernando, Dr Jim McMorran BM BCh PhD DCH DRCOG MRCGP FRCGP

In this episode, Dr Kevin Fernando and Dr Jim McMorran discuss the ongoing NHS-Galleri trial. The study, which is being conducted among 140,000 asymptomatic patients in England, will assess whether the new Galleri blood test can assist in detecting cancer early when used alongside existing screening measures in the NHS. Kevin and Jim consider the sensitivity, specificity and positive predictive value of the test, reflect on how the test compares with other investigative measures for cancer and contemplate the key practical aspects primary care professionals should be aware of.


Key references discussed in the episode:

Key resources:

Key take-home points:

  • The NHS-Galleri trial represents a screening tool that hopes to identify multiple cancers. In contrast, existing national cancer screening programmes are site-specific (e.g., bowel or cervix).
  • The Galleri technology has the potential to identify cancers in the early stages and when asymptomatic.
  • If a patient has a positive Galleri test, the positive predictive value for cancer is about 40% (i.e., 40% of patients who have a positive test will have a cancer).
  • Based on previous studies, the Galleri tool identifies about 44% of stage I–III cancers. Also, the study design of the NHS-Galleri trial means that 50% of patients recruited will not have the test. The combination of these two facts means that the trial will identify less than a quarter of the stage I-III cancers in the study population.
    • Therefore, GPs who have patients in the study cannot assume that a patient without a positive test does not have cancer and should manage their patients with the usual safety netting.
  • Patients involved in the NHS-Galleri trial should be encouraged to continue to partake in national cancer screening programmes.

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