Dr. Kyle Mikals, MD, FACP | Jacksonville Concierge Medicine
Over the past year, more patients have asked me about blood tests that claim to screen for dozens of cancers at once. The idea is simple: one tube of blood, drawn before you have any symptoms, checked for signs of many different cancers. These are called multi-cancer early detection (MCED) tests. The two you’ll hear about most are Galleri, made by GRAIL, and Cancerguard, made by Exact Sciences (the company that makes Cologuard).
I think these tests are worth understanding, so here’s what I tell patients when they ask: how the two tests differ, how accurate they are, where they stand with the FDA, and whether I’d recommend one right now.
Why these tests exist
We only have routine screening for a handful of cancers: breast, cervical, colon, lung (for people at high risk), and prostate (as an individual decision). Most cancer deaths come from cancers with no screening test at all (Matrana et al., Nature Communications, 2025).
MCED tests try to fill that gap. Cancers shed tiny fragments of DNA and other signals into the blood, and these tests look for them. The hope is to catch cancer earlier, when it may be easier to treat.
One point I want to be clear on up front. These tests are meant to be added to your regular screenings, not to replace them (Rubin, JAMA, 2024). If you’re due for a mammogram, colonoscopy, Pap smear, or lung CT, a blood test doesn’t take its place.
How Galleri and Cancerguard differ
Galleri looks at methylation patterns, which are chemical “tags” on DNA floating in the blood. It’s designed to pick up a signal from more than 50 types of cancer. If it finds one, it also predicts which organ the cancer is likely coming from, which helps guide the next steps. Galleri is by far the most studied MCED test, including the first large randomized trial.
Cancerguard combines several signals: DNA mutations, methylation changes, and proteins in the blood. It’s newer and has much less large-scale published data. Earlier research (under the name CancerSEEK) focused on a smaller group of cancers.
Both are a simple blood draw, both need a prescription, and both are meant to go alongside standard screening.
How accurate are they?
Two terms matter here. Sensitivity is how often a test finds cancer when cancer is really there. Specificity is how often it correctly comes back negative in people who don’t have cancer. Both tests have very high specificity, around 99%, so false alarms are uncommon. They do happen, though.
Sensitivity is where things get more complicated. It depends a lot on the type of cancer and how far along it is. Advanced cancers shed more DNA into the blood, so they’re much easier to find than early ones. That’s the opposite of what we’d ideally want from a screening test.
Galleri
In the main validation study, Galleri found about 51% of cancers overall, with 99.5% specificity (Klein et al., Annals of Oncology, 2021). Broken down by stage, it caught roughly 17% of stage I cancers, 40% of stage II, 77% of stage III, and 90% of stage IV.
It does best with 12 aggressive cancers that cause about two-thirds of U.S. cancer deaths, including pancreas, liver, esophagus, ovary, and lung. For that group, sensitivity was about 76%. It does poorly with some common cancers. It found about 31% of breast cancers and about 11% of prostate cancers, and it didn’t detect thyroid cancer in the study.
The PATHFINDER 2 study looked at how the test performs in real-world use in over 32,000 people. Galleri found about 39% of all cancers that showed up within a year, and about 70% of the 12 high-risk types. When the test was positive, it was right about 60% of the time, and it predicted the correct organ of origin in about 91% of cases (Nabavizadeh et al., Nature Medicine, 2026).
Cancerguard
There’s far less large-scale data on Cancerguard. In earlier research, it detected roughly 69% to 98% of liver, stomach, pancreas, esophageal, and ovarian cancers, with specificity above 99% (Grady, Digestive Diseases and Sciences, 2025). Like Galleri, it was much less reliable at stage I. Detection was high for liver cancer, for example, but only around 20% for esophageal cancer.
What the results mean
A negative result doesn’t mean you’re cancer-free. A positive result isn’t a diagnosis. It means you’ll need more testing, often imaging or a biopsy, to find out whether cancer is actually there.
Where they stand with the FDA
Neither Galleri nor Cancerguard is FDA-approved. Both are sold as “laboratory-developed tests,” a separate and less rigorous pathway (Hoffman et al., Cancer, 2025). No major medical guideline recommends them for routine screening right now, and insurance usually doesn’t cover them. Out-of-pocket cost typically runs from $600 to $1,000.
It’s also worth knowing that when the FDA does review tests like these, it looks at how accurately they detect cancer. It doesn’t look at whether they help people live longer.
Would I recommend one right now?
The promise of these tests hasn’t been backed up yet by proof that they save lives.
The largest randomized trial of Galleri so far, the NHS-Galleri study in England, enrolled about 142,000 people. It didn’t meet its main goal of reducing the number of cancers caught at an advanced stage (Sasieni et al., New England Journal of Medicine, 2026). The test did find more early-stage cancers, and some cancers that have no other screening test. And false-positive results didn’t seem to cause lasting anxiety (Marinac et al., Nature Medicine, 2026). Longer follow-up is still underway.
No completed study has shown that MCED testing lowers the chance of dying from cancer (Kahwati et al., Annals of Internal Medicine, 2025). A positive result can also lead to a series of scans and procedures, each with its own cost, risk, and stress, and sometimes no cancer is found at the end of it.
So my advice is this. Stay current on your proven screenings first, because mammograms, colonoscopies, Pap smears, and lung CTs save lives. If you’re especially worried about cancers we can’t screen for, particularly if you’re at higher risk, an MCED test may be worth discussing, with the understanding that the benefit isn’t proven yet. It’s a personal decision that depends on your risk, the cost, and how you’d handle a false alarm or an uncertain result (Selby et al., Annals of Internal Medicine, 2023).
Questions to ask before you test
- Am I up to date on all my recommended cancer screenings?
- Given my personal and family history, would this test tell us anything useful?
- If the result is positive, what happens next, step by step?
- What will it cost me out of pocket?
- How would I handle a result that turns out to be a false alarm?
My Final Thoughts
Galleri and Cancerguard are an exciting step toward screening for many cancers with one blood test. Today, though, neither is FDA-approved, recommended by guidelines, usually covered by insurance, or proven to help people live longer. The tests mostly detect cancer at stage 3 or 4, which is already a little too late. If you’re curious about one, treat it as a possible add-on to your regular screenings, never a replacement, and talk it through with your doctor first.
