Multi-cancer blood tests

Don't buy a multi-cancer blood test as a routine screen outside a trial. It does not replace the proven tests for bowel, breast, cervical and lung cancer, and national screening bodies want evidence of fewer cancer deaths before recommending it.

What they are, and the gap they aim at

These tests, called multi-cancer early detection (MCED) tests, read chemical tags on DNA that tumours shed into the bloodstream. The appeal is real: about two-thirds of cancer deaths come from cancers with no recommended screening test at all. That is 68.6% on the one published estimate, produced by authors five of whom work or worked for a company selling one of these tests.^[1]

How accurate they are

A systematic review for the UK National Institute for Health and Care Research found 36 studies of how well these tests perform and no completed randomised trial. Most studies were at high risk of bias, chiefly because people who tested negative were rarely followed up to see whether they had cancer after all. Galleri caught between 21% and 66% of cancers across studies, while correctly clearing 98.4–99.5% of people without cancer. The review described these figures rather than pooling them, and its searches closed in September 2023.^[2]

The NHS-Galleri trial: mixed results

The first large randomised trial enrolled over 142,000 people aged 50 to 77 without symptoms in England. Its main results were presented at the 2026 American Society of Clinical Oncology meeting and are not yet published in a peer-reviewed journal, so the figures come from a conference abstract and from the manufacturer's own account of its trial.^[3]

• Main goal missed. Late-stage (stage III or IV) cases of 12 pre-specified cancers were no fewer: 706 in the tested group against 688 in the control group. Stage IV alone, a secondary measure, was about 14% lower, with a margin of uncertainty that only just excludes no effect.
• More early cancers. Early-stage (stage I or II) diagnoses were 16% higher, 647 against 559, and about four times as many cancers were found by screening, 1,173 against 290, when the test was added to standard screening.
• Fewer emergency diagnoses. Cancers diagnosed as emergencies fell by 21% in the abstract, 225 against 286; the manufacturer's own account says 25%.
• Few false alarms. After three yearly rounds, only about 1.2% of the tested group were sent for investigation without a cancer being found, and 52% of positive results turned out to be cancer.^[4]

Why earlier-stage diagnoses aren't enough

Finding more early-stage cancers without preventing late-stage ones fits detecting slow-growing cancers faster rather than dangerous ones earlier. The UK National Screening Committee says an earlier stage is a stand-in (surrogate) outcome, trustworthy only once it has been shown to track the outcome that matters, and that surrogates "cannot yet replace mortality as the definitive trial outcome for benefit".^[5] Its 2026 position is that these tests need adequately powered randomised evidence of fewer cancer deaths before they can be recommended for population screening.^[6] Professional oncology societies took the same line in 2026; the US Preventive Services Task Force has issued no position at all.

That evidence has a date: the NHS-Galleri protocol schedules its cancer-death analysis about two years after the stage results, so around 2028.^[7]

A cost accuracy can't capture

Screening healthy people competes for the scanners and clinics that people with symptoms are waiting for. In the English regions that hosted the trial, the share of urgent referrals for suspected head and neck, lung and upper gut cancer taking more than 28 days to reach a diagnosis rose while it fell everywhere else: by about 3 percentage points in the first six months and 5 in the next. The effect was no longer significant after the first year.^[8] That is an argument about health-system capacity rather than about the test.

What to do

1. Do the proven screens first. The tests with trial evidence, and their schedules, are on Cancer screening.
2. Treat a multi-cancer test as research, not a check-up, until a trial shows fewer cancer deaths; the first answer is due around 2028.
3. If you take one anyway, keep up your routine screens. Across studies Galleri caught only 21–66% of cancers.

Further reading

• Batson S et al. UK National Screening Committee position statement on evidence required for multicancer detection tests. BMJ 2026.^[9]
• NHS-Galleri trial — topline results. GRAIL press release, 2026.^[10]