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How Accurate Is Galleri, and What Do Its Results Mean?

Galleri rarely gives a false alarm, but it misses many cancers, especially early ones. Here is what its published sensitivity, specificity and predictive value mean, and what each result tells you.

Published

October 20, 2026

Read time

13 min read

Medically reviewed by

Rhonda Collins, FNP-C

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Galleri is very good at not raising false alarms, and it misses a large share of cancers. In the largest US study, PATHFINDER 2, about 6 in 10 people with a positive result were found to have cancer, and only 0.36% of people without cancer got a false positive. But the test flagged only about 4 in 10 of the cancers diagnosed in the following year, and in GRAIL’s case-control study it caught just 16.8% of stage I cancers. So “how accurate is Galleri?” has two honest answers: a positive result deserves to be taken seriously, and a negative result should not change any other screening you do.

This article explains the accuracy measures in plain language, what each study found, and what the two possible results mean. For background on how these tests work, see what a multi-cancer early detection test is.

Why “99% accurate” is the wrong way to describe Galleri

No single number describes a cancer screening test. Galleri is often summed up by its specificity, which is above 99%, but specificity only describes people who do not have cancer. Three different measures answer three different questions:

• Sensitivity asks: of the people who have cancer, what share get a positive result? Low sensitivity means missed cancers (false negatives).
• Specificity asks: of the people who do not have cancer, what share get a negative result? High specificity means few false alarms (false positives).
• Positive predictive value (PPV) asks: of the people who get a positive result, what share actually have cancer? This is the number that matters most once you hold a positive report.

A test can have very high specificity and still miss many cancers. In GRAIL’s CCGA3 validation study, specificity was 99.5%, but the test detected 51.5% of the cancers.

There is a second distinction. Test sensitivity comes from case-control studies, where researchers already know who has cancer. Episode sensitivity comes from screening studies: it counts how many of the cancers diagnosed within a set period (usually 12 months) the test had flagged. The PATHFINDER 2 authors say the two should not be compared directly, because they come from different populations with different mixes of cancer types and stages.

What GRAIL’s studies found

Each figure below belongs to one study, one population and one version of the test. Do not combine them.

CCGA3 reports test sensitivity. PATHFINDER 2 and NHS-Galleri report episode sensitivity, the share of cancers diagnosed within 12 months of a test that the test had flagged. The 12 deadly cancers are a prespecified group that GRAIL says accounts for about two-thirds of US cancer deaths.

CCGA3 (Klein and colleagues, Annals of Oncology, 2021 [1]) validated the version of the test that GRAIL refined for screening. It enrolled 4,077 people whose cancer status was known. Because about two-thirds of them already had cancer, this study measures how well the test reads a cancer signal. It cannot tell you how often a positive result is right in an ordinary screening population, so it has no PPV.

PATHFINDER 2 (Nabavizadeh and colleagues, Nature Medicine, 2026 [2]) is the closest match to someone ordering Galleri today: adults 50 and older with no symptoms or suspicion of cancer, tested once and followed for a year. Of 32,007 people analyzed, 287 (0.9%) had a positive result and 173 of them were diagnosed with cancer. In the same year, 267 people were diagnosed with a cancer the test had not flagged. The authors note that the study used an earlier version of the test, since replaced by a commercial version that predicts one signal origin instead of two.

NHS-Galleri is covered in its own section below.

An earlier US study, PATHFINDER [3], tested 6,621 adults 50 and older. A cancer signal was detected in 92 people (1.4%), and 35 of them (38%) were diagnosed with cancer. Its results come from the first years of the test’s use in screening.

Galleri detects early-stage cancer far less often

Galleri is much better at finding advanced cancer than early cancer. In the CCGA3 validation, sensitivity rose sharply with stage:

Source: Klein and colleagues, Annals of Oncology, 2021 [1].

This matters because the main reason to screen is to find cancer early. The test works by reading DNA that tumors shed into the blood, and small, early tumors shed less. The National Cancer Institute makes the same point about the whole category: current data indicate that these tests are better at detecting later-stage cancer than early-stage disease [4].

Detection also varies widely by cancer type. GRAIL reports its highest sensitivity for aggressive cancers such as liver and bile duct, pancreatic, esophageal and ovarian cancer, and its lowest for common, slower-growing ones. In GRAIL’s published case-control figures [5], it detected 30.5% of breast cancers, 11.2% of prostate cancers and none of the thyroid cancers. GRAIL’s results guide [6] also lists brain, skin, and early-stage breast and prostate cancers among those unlikely to be found by a blood test. That is why mammograms, colonoscopy, cervical screening and, where eligible, lung CT stay in place.

A low false-positive rate does not make every positive result cancer

Galleri’s false-positive rate is low, but around 4 in 10 positive results in the US screening study still turned out not to be cancer. Both facts are true because cancer is uncommon in people without symptoms, so even a small false-alarm rate across thousands of healthy people adds up.

PATHFINDER 2 makes this concrete. Scaled to 1,000 people tested (derived from the study’s counts):

• about 9 would get a “cancer signal detected” result;
• about 5 of those 9 would be diagnosed with cancer;
• about 4 would have a full workup and no cancer found;
• about 8 more people would be diagnosed with a cancer within the year that the test did not flag.

The NHS-Galleri trial reported the same pattern in its own words: if 200 people had the test, two would get a positive result, and one of those two would be diagnosed with cancer [7].

A false positive is not harmless. In PATHFINDER 2, 213 of 35,335 participants (0.6%) had an invasive procedure, such as a biopsy, after a positive result; 90.5% of those procedures were nonsurgical, and no serious study-related adverse events were reported. In the first PATHFINDER study, people with a false positive took a median of 162 days to reach a final answer, compared with 57 days for people whose positive result was cancer.

What a “Cancer Signal Detected” result means

A “Cancer Signal Detected” result means the lab found a DNA methylation pattern associated with cancer. It is not a diagnosis. It comes with a predicted Cancer Signal Origin, the tissue or organ the signal most likely came from, so your doctor knows where to look first.

The signal origin prediction is usually right when cancer is present. Among people whose positive result was confirmed as cancer, it matched the actual site in 88.7% of cases in CCGA3, 91.3% in PATHFINDER 2 (counting either of two predictions) and 92.5% in NHS-Galleri. It does not tell you whether cancer is present, only where to start looking if it is.

What happens next, according to GRAIL’s guide to results [6]:

1. Your clinician orders diagnostic tests. These usually start with lab work or imaging aimed at the predicted origin, and may lead to a biopsy.
2. The workup confirms cancer or does not. In PATHFINDER 2, about 60% of people with a positive result were diagnosed with cancer.
3. If no cancer is found, it may mean there is no cancer, or that the testing did not find it, including because the cancer is somewhere other than the predicted site. Your doctor decides whether more testing or monitoring makes sense.

GRAIL states that the price of the Galleri test does not include this diagnostic testing.

What a “No Cancer Signal Detected” result means

A “No Cancer Signal Detected” result means the test did not find a cancer signal in that sample. It does not rule out cancer. Nearly 99% of people who take Galleri get this result, according to GRAIL, but in PATHFINDER 2 more than half of the cancers diagnosed during the following year came after a negative test.

A negative result does not change anything else you do:

• keep every screening your doctor recommends, on schedule;
• do not ignore new symptoms because of a recent negative result;
• remember that it describes your blood at the time of the draw only. Galleri does not test for inherited gene variants and does not predict future cancer.

Because a negative result covers only that one draw, the timing of the next test is its own question. See how often to take the Galleri test.

What the NHS-Galleri trial found

NHS-Galleri is the only randomized controlled trial of Galleri, and it did not meet its main goal. It enrolled 142,250 people aged 50 to 77 in England and randomly assigned them either to standard NHS screening alone or to standard screening plus three yearly Galleri tests. The trial’s primary question was whether adding Galleri would reduce the number of stage III and stage IV cancers combined, in 12 prespecified aggressive cancer types. It did not: the rate was essentially the same in both groups (incidence rate ratio 1.03, with a 95% confidence interval of 0.92 to 1.14).

The secondary findings, reported by GRAIL at the 2026 ASCO Annual Meeting [8]:

• Fewer stage IV cancers. For the same 12 cancer types, stage IV diagnoses were 14% lower in the Galleri group over three rounds. By round, they were 9% lower in the first round, 22% lower in the second and 26% lower in the third. GRAIL describes the overall result as nominally statistically significant. The first- and second-round confidence intervals include no difference, so the round-by-round trend is less certain than the headline percentages suggest.
• More early-stage cancers. Stage I and II diagnoses of those 12 cancers rose by 16%.
• More stage III cancers, particularly in the first round. GRAIL says this increase outweighed the stage IV reduction, which is why the combined stage III and IV result showed no reduction.
• Accuracy in the test group: 0.91% of people had a positive result, 52.0% of positives were diagnosed with cancer, and the false-positive rate was 0.45% [9].

These are conference results. GRAIL says the trial will be submitted to a peer-reviewed journal, and follow-up continues.

Finding cancer earlier is not the same as living longer

No study has shown that Galleri reduces cancer deaths or helps people live longer. The research asks three different questions, and only the first has a clear answer:

1. Does the test detect cancer? Yes, for many cancers, with the limits described above.
2. Does it shift diagnoses to earlier stages? NHS-Galleri found fewer stage IV and more stage I and II diagnoses, but missed its primary stage III and IV endpoint.
3. Does it reduce deaths from cancer? Not yet known. The NHS-Galleri team lists effects on cancer deaths among the questions still being studied.

The National Cancer Institute’s position is that no definitive clinical trials have shown that multi-cancer detection tests reduce cancer deaths [4], and that neither professional medical societies nor the U.S. Preventive Services Task Force have issued recommendations on their use. Galleri is not part of any major screening guideline.

On regulation: GRAIL submitted a premarket approval application in January 2026, and on September 23, 2026, an FDA advisory panel voted 6 to 4 that the test is effective, 7 to 2 with one abstention that its benefits outweigh its risks, and unanimously that it is safe [10]. A panel vote is advice. As of October 20, 2026, the FDA had not made a final decision, and GRAIL’s own materials state that the test has not been cleared or approved by the FDA.

How to read your Galleri report

If you already have a result, or are deciding whether to order the test, these questions get you the most out of it.

If your result is “Cancer Signal Detected”:

• What is the predicted Cancer Signal Origin, and what is the first test to look there?
• Is there anything in my history, symptoms or past results that points the same way?
• If the first tests find nothing, what is the plan: more imaging, a different site, or a repeat test later?
• What will the workup cost, and what will insurance cover? The Galleri price does not include it.

If your result is “No Cancer Signal Detected”:

• Which screenings am I due for, and are they booked?
• Which of my personal risk factors does this test cover poorly (for example, breast or prostate cancer)?
• When, if at all, would a repeat test make sense for me?

When you order Galleri through Mito, the blood is drawn at a partner lab, the result lands in your Mito dashboard next to your other bloodwork, and a clinician reviews it. You can book a video consult with the Mito care team to go through these questions. A positive result still needs a diagnostic workup ordered by your own doctor or a specialist.

To compare Galleri with the other test Mito offers, see LucenceINSIGHT vs. Galleri. For what these tests cost and how to order one, see multi-cancer blood test cost and the multi-cancer early detection test guide.

References

1. Klein EA et al. Clinical validation of a targeted methylation-based multi-cancer early detection test using an independent validation set. Ann Oncol. 2021.
2. Nabavizadeh et al. Performance and safety of a multi-cancer early detection test: the PATHFINDER 2 study. Nature Medicine. 2026.
3. Schrag D et al. Blood-based tests for multicancer early detection (PATHFINDER): a prospective cohort study. Lancet. 2023.
4. National Cancer Institute: Questions and Answers about Multi-Cancer Detection Tests
5. Galleri: Galleri Test Sensitivity & Specificity
6. Galleri: Understanding Your Galleri Test Results
7. NHS-Galleri Trial: How accurate was the test?
8. GRAIL: GRAIL Reports Full Results From NHS-Galleri Trial Demonstrating Substantial Reduction in Stage IV Cancer Diagnoses at 2026 ASCO Annual Meeting
9. NHS-Galleri Trial: What the trial found
10. GRAIL: FDA Advisory Committee Votes in Favor of Approval of GRAIL’s Galleri Multi-Cancer Early Detection Test

Frequently asked questions

Is the Galleri test FDA approved?

Not as of October 20, 2026. GRAIL submitted a premarket approval application in January 2026, and an FDA advisory panel voted in favor on September 23, 2026, but a panel vote is advice, not approval. Galleri is offered as a laboratory-developed test that GRAIL states has not been cleared or approved by the FDA.

Is the Galleri test worth it if it misses so many cancers?

That depends on what you want from it. Galleri adds a check for many cancers that have no routine screening, with a low false-alarm rate, but it misses most early-stage cancers and has not been shown to reduce cancer deaths. It is designed to sit on top of guideline screening, not to replace it.

Can Galleri detect pancreatic cancer?

It can. Pancreatic cancer is one of the 12 cancer types GRAIL highlights, and in GRAIL's published case-control figures the test detected 83.7% of pancreatic cancers across all stages. Detection is lower for early-stage tumors, so a negative result does not rule pancreatic cancer out.

How long does it take to get Galleri results?

GRAIL says results are usually available about two weeks after the sample reaches its lab. When you order through Mito, the result appears in your Mito dashboard once the lab releases it.

Does a Galleri result tell me my risk of getting cancer later?

No. Galleri looks for a cancer signal in your blood at the time of the draw. It does not test for inherited gene variants and does not predict whether you will develop cancer in the future.

Does the price of Galleri cover the tests after a positive result?

No. GRAIL states that the cost of the Galleri test does not include the diagnostic testing needed to confirm cancer. Imaging, biopsies and specialist visits after a positive result are billed separately, and coverage depends on your insurance plan.