How Accurate Are MCED Tests?

"Accuracy" isn't a single number. To understand how well an MCED test performs, it helps to know four terms:

• Sensitivity — how often the test correctly flags people who do have cancer. High sensitivity means fewer missed cancers.
• Specificity — how often the test correctly clears people who don't have cancer. High specificity means fewer false alarms.
• False-positive rate — how often the test signals cancer in someone who doesn't have it.
• Positive predictive value (PPV) — of the people who get a positive result, the share who actually turn out to have cancer.

A good screening test needs to balance all four.

This is the biggest catch. MCED tests are much better at detecting later-stage cancers than early ones.

In GRAIL's large validation study, overall sensitivity across cancer types was about 51.5%, but it rose sharply with stage: roughly 17% for stage I, 40% for stage II, 77% for stage III, and 90% for stage IV. [2] A 2025 systematic review found a similar pattern, with sensitivity around 37% for stage I–II cancers versus about 90% for stage III–IV. [3]

In plain terms: MCED tests catch most advanced cancers but miss many early-stage ones, which is a real limitation given that the whole point is to find cancer early.

Here MCED tests shine. Studies consistently report specificity around 99.5%, meaning only about 0.4% to 0.5% of people without cancer get a false-positive result. [2] [4] Systematic reviews confirm high specificity (generally above 96%) across the tests studied. [3]

A low false-positive rate matters because it reduces unnecessary anxiety and follow-up procedures.

MCED tests don't detect every cancer equally well. Sensitivity is higher for the most aggressive cancers, for example, one analysis found about 67.6% sensitivity for stage I–III among the 12 cancer types responsible for roughly two-thirds of U.S. cancer deaths. [4] For some other cancer sites, detection of early-stage disease can be much lower. [3] So an MCED test may be quite good at flagging one cancer and less reliable for another.

This is where positive predictive value comes in, and where the tests are improving.

In the PATHFINDER study published in The Lancet in 2023, the Galleri test's PPV was about 43%, meaning fewer than half of people with a positive result actually had cancer. [4] That aligns with the American Cancer Society's note that, so far, over half of positive MCED results turn out to be false positives after further testing. [1]

Newer data looks better. In the PATHFINDER 2 study presented in 2025, the updated test's PPV improved to about 62% (roughly six in ten positives were true cancers), with a false-positive rate of just 0.4%. Notably, adding the test to standard screening detected more than seven times as many cancers, and fewer than 1% of all participants underwent an invasive procedure because of the test. [5]

When an MCED test detects a signal, many can also predict where in the body the cancer likely started, called the cancer signal origin. Accuracy for this prediction is high, around 90% in studies, which helps doctors direct follow-up testing efficiently. [4] [5]

High sensitivity and specificity are encouraging, but they don't automatically prove that MCED tests help people live longer. It is not yet known whether MCED testing actually reduces cancer deaths.^[1]

The strongest evidence to date comes from the NHS-Galleri trial in the United Kingdom, the first and only randomized, controlled trial of an MCED test. It followed about 142,000 participants aged 50 to 77 over three years, with full results reported at the 2026 ASCO Annual Meeting. Adding annual MCED screening to standard care led to a four-fold increase in screen-detected cancers and a greater than 20% reduction in stage IV (advanced) cancer diagnoses by the third year of screening, along with more early-stage (stage I and II) diagnoses of hard-to-catch cancers such as ovarian, pancreatic, and liver.^[6]

What This All Means for You

Putting it together:

• MCED tests rarely raise a false alarm (high specificity), which is a real strength.
• They catch most late-stage cancers but miss many early ones (variable sensitivity), which is their main limitation.
• A positive result is not a diagnosis and always requires follow-up testing.
• A negative result is reassuring but not a guarantee, so keep up your recommended screenings and report any new symptoms.
• These tests are not yet FDA-approved; they are offered as lab-developed tests a provider can order.^[1]
• They add to, and do not replace, proven screenings like mammograms, colonoscopies, and Pap tests.^[1]

Because of these nuances, deciding whether an MCED test is right for you is best done with your doctor, weighing your personal risk, your willingness to pursue follow-up testing, and the current limits of the evidence.

MCED technology is advancing quickly, and it offers a promising new way to look for many cancers from a single blood draw, as one layer of a broader proactive health plan.

Everlywell now offers the Caris Detect multi-cancer early detection test, which screens for a signal shared by more than 50 types of cancer from a single blood draw, along with genetic counseling to help you understand your results. Talk with your doctor about whether an MCED test fits your risk and goals, and keep up with your standard screenings.