A signal is not a diagnosis
A positive screening result may lead to further investigations to find out whether cancer is present and where it might be. It does not, by itself, establish the diagnosis, stage or appropriate treatment.
Those investigations can involve scans, endoscopy or tissue sampling, depending on the findings. A biopsy answers a different question from a screening blood test.
A signal may also be found when cancer is not subsequently confirmed. Follow-up can therefore bring uncertainty as well as additional tests and their possible harms.
A negative result cannot rule out every cancer
No screening test detects every cancer. Performance may differ by cancer type and stage. A result that does not detect a cancer-associated signal is not a guarantee that cancer is absent.
New or persistent symptoms still need appropriate assessment. A previous negative screening result should not be used to explain away a symptom or replace a clinical investigation.
Finding cancer is not the only outcome that matters
Screening is offered to people who do not have symptoms suggesting the condition being screened for. To judge a programme, researchers consider both benefits and harms across that population.
Detecting more cancers, or finding them at an earlier stage, is not on its own proof that testing reduces deaths. Follow-up studies need to examine meaningful outcomes and the effects of false results, extra investigations and overdiagnosis. Overdiagnosis means identifying a cancer that would not otherwise have caused illness during that person's life.
If you are considering a test
Ask who the test is intended for, what evidence supports its use and what follow-up is available after an uncertain or positive result. Clarify costs and responsibilities for further investigations where relevant.
Do not assume a multi-cancer blood test replaces established screening invitations or tests arranged for symptoms. In the UK, your GP can discuss concerns and the screening programmes for which you are eligible.
General information only, not a recommendation for a particular test. If investigations lead to a diagnosis, this guide explains the next steps.
