A result exists and a destination does not, and that is the hardest situation these tests create. In people with no symptoms, most positive results turn out to be false — and proving that takes longer than finding a cancer would. There is currently no agreed answer to how closely someone in this position should be followed, and anyone who offers one with confidence is going beyond the evidence. What can be done is to close the chest half of the question properly, with a defined interval and a defined end point. Dr Lawrence Okiror, Consultant Thoracic and Robotic Surgeon (GMC 6150382). Appointments at London Bridge Hospital and The Lister Hospital Chelsea within 2–3 days, including video consultations. Self-referrals welcome.
Last reviewed: August 2026 · Dr Lawrence Okiror FRCS(CTh) FRCSEd(CTh) · GMC 6150382
In a well population, serious disease is uncommon — so even a very accurate test raises more false alarms than true findings. That is arithmetic, not a fault in the test.
In the largest published experience, resolving a positive took around two months where a cancer was found and around five where none was, with a quarter waiting eight months or longer.
The chest half can be closed properly: what is being watched, with what test, at what interval, and at what point the matter is considered finished. Not an open-ended arrangement to keep scanning.
Almost every other test in medicine hands you on to someone. An abnormal liver test goes to a hepatologist. A suspicious mammogram goes to a breast clinic. A positive multi-cancer blood test in a well person with normal imaging goes nowhere in particular, because it does not name an organ, a specialty or a pathway. You are left holding a result that has no obvious owner.
That is not a failure of the people you have seen. The situation is genuinely new, it falls between specialties by design, and the published literature is explicit that the right follow-up is not yet known. Being told there is no clear answer is unsatisfying, but it is more useful than being given a confident one that has nothing behind it.
What follows is what these tests measure, what a positive result can and cannot tell you, what the evidence actually shows about resolving one, and what can be settled about the chest. For the imaging side of the same problem — a scan that has found something rather than a blood test — see a scan or blood test has flagged something in your chest.
Tests sold under similar names work in quite different ways, and what a positive means differs between them. Two broad kinds account for almost everything on sale.
One point of practical confusion is worth clearing up. Galleri is the test most people have heard of, because of the large NHS trial that reported in 2026. Until recently it was available in the UK only within that trial; it carries a UKCA mark and began to be offered privately here during 2026 through a small number of clinical providers, though it remains unavailable on the NHS. UK clinics also sell several other tests, and because the reporting language is similar, people frequently believe they have had Galleri when they have not. Bring the actual report rather than the brand name — the difference matters to how the result should be read.
This is the part that most changes how a result should feel, and it has nothing to do with the quality of the test. It is about who the test was given to.
Imagine a very accurate test applied to a large group of well people. Serious cancer is uncommon in such a group. The small number of people who do have a cancer will mostly be picked up. But the very large number who do not have one will produce a small proportion of incorrect alarms — and because that group is so much bigger, that small proportion can easily outnumber the true findings. The result is that in people without symptoms, a positive is more often wrong than right.
The same arithmetic applies to every screening test ever devised, including the national programmes, which is why those programmes are offered to defined groups at defined ages rather than to everyone. It is the reason screening is targeted rather than universal, and it is a feature of screening rather than a flaw in any particular product.
What it does mean is that a positive result in a well person is a reason to investigate carefully, not a reason to assume the worst. And it means the sensible response to a clear scan is considerable reassurance rather than a search for what the scan must have missed.
There are other explanations for a positive result besides cancer. Some benign conditions of the blood and bone marrow produce the same signals; in one reported series a substantial share of false positives were traced to a benign condition of the white blood cells. Where a positive result is unexplained after imaging, a haematology opinion is sometimes the more useful next step than another scan.
Longer when nothing is found than when something is, which is the opposite of what most people expect and the single most useful thing to know in advance.
In the largest published experience of a multi-cancer blood test used in this way, the time taken to reach a resolution was around two months where a cancer was eventually diagnosed, and around five months where none was. A quarter of people waited eight months or longer. A later and considerably larger study reported shorter times overall, so the picture is improving — but the shape of it does not change. Finding a cancer ends the question. Proving there is no cancer has no equivalent moment.
That asymmetry is the real cost of these tests, and it is not measured in money. It is months of a well person's life spent inside an unresolved question. Knowing that in advance changes how the waiting feels, and it is a strong argument for a plan with a stated end point rather than an open arrangement to review things periodically.
The reassuring counterweight from the same body of work: very few people in these studies ended up having an invasive procedure as a consequence, and of those who did, the great majority were not operations.
No. And that deserves to be said in one word rather than dressed up.
Published analysis of exactly this situation states that individuals with risk factors whose first round of investigation comes back negative or equivocal remain at some risk of a cancer diagnosis later, and that uncertainty remains as to how closely such people should be followed. It is unusual for a scientific paper to concede that so directly, and it should be taken at face value. Anyone offering you a confident surveillance schedule for this situation is going beyond what is known.
Blood tests for cancer DNA are also used in people who already have a diagnosed cancer, to look for traces remaining after treatment. That is a much easier problem — the cancer is known and the target is defined. Even there, the European Society for Medical Oncology states that current assays give information about outlook but not about which treatment will work, that sensitivity is suboptimal with a large proportion of false negatives, and recommends against using them to guide treatment decisions outside clinical trials.
That is not a statement about screening tests in well people, and it should not be presented as one. But if the technology is not yet considered ready to guide decisions in the situation where the answer is known, it is worth holding that in mind when a result arrives in someone entirely well.
What can be done, in the absence of a protocol, is to make the plan explicit. What is being watched. With what test. At what interval. And at what point the matter is considered closed. A plan with those four elements is worth more than a confident-sounding schedule with nothing behind it.
It is the natural response and it is usually the wrong one. Repeat whole-body imaging of a well person mostly produces further incidental findings rather than an explanation for the original result. Each of those findings then needs its own assessment. Some lead to procedures. And the original question stays exactly where it was.
The more useful approach runs in the other direction: go narrow rather than wide. Identify anything in the imaging you already have that is genuinely equivocal. Characterise that one thing properly with a targeted test aimed at the specific question. Then set a defined interval with a defined end point for anything that remains uncertain, and stop.
One further point about the chest specifically. If lung cancer is the concern behind all this, the scan that answers it is a CT. A whole-body MRI is progressively unreliable for small lung nodules and a chest reported as clear on one has not had its lungs examined to CT standard. That is set out in detail on the chest finding page, and what a lung nodule is and how it is assessed on the lung nodule page.
Take responsibility for the chest half, and close it properly. That is a narrower offer than you might want, and it is the one I can make honestly.
Reviewing the imaging itself rather than the report, because reports are written to be defensible and often sound more equivocal than the pictures are. Deciding whether anything in the chest genuinely needs characterising, and arranging the one targeted test if it does. And setting a defined interval and a defined end point, so that this stops being an open question.
Where the honest answer is that nothing in the chest requires anything at all, that is what you will be told — plainly, and with the reasoning, so that it holds up when the worry comes back at three in the morning.
What I will not do is take on the findings outside the chest. These investigations routinely produce results in the liver, kidneys, adrenal glands, prostate, spine and brain, and working outside my specialty would not serve you. I will tell you which of them look as though they warrant a specialist opinion and which are the common harmless ones, rather than leaving you to work that out from a report.
And I will not offer a view on whether you should have had the test. People choose these deliberately, usually after reading a great deal, and being told afterwards that it was a mistake helps nobody. My involvement starts at the point the result exists. Where a case is genuinely uncertain it is discussed at the chest multidisciplinary team meeting, and if you have already been given an opinion you are unsure about, a second opinion is a reasonable thing to want.
The statements on this page are written without technical vocabulary. The underlying figures are set out here in full.
Questions people ask after a multi-cancer or circulating tumour cell blood test has returned a positive result and the imaging has found nothing.
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