How often do full-body MRIs find cancer?

2/14/2026 at 9:37:31 PM

“ One study in 2020 found that 95% of asymptomatic patients had some type of "abnormal" finding, but just 1.8% of these findings were indeed cancer.”

This has been my experience. And I’ve had oncologists echo exactly this. In the words of one: MRIs find too much.

The CT and the PET/CT are the gold standards for finding cancer, finding recurrences, and staging cancer. The trouble is the radiation dose.

MRI provides very inconclusive results. You’ll see something but it’ll be unclear what it is. And often what you see is not even visible on a CT. Or it’s visible on a PET/CT and is showing metabolic activity indicating its cancer.

MRIs are great for certain things like herniated disks in your back. They suck at cancer.

by mmaunder

2/14/2026 at 10:14:13 PM

Spot on. And dealing with false positives sucks.

One caveat is that regular PET isn't so good in the brain - there is so much metabolic activity that everything glows. So I get an MRI Brain to go with my regular full body PET/CT (cancer 5 years ago with recurrence 18 months later, currently NED).

by mcbain

2/14/2026 at 10:18:58 PM

I had a CT scan last year for some stomach issues they wanted to look at.

Doctor warned me up front that the odds the images find something that looks weird is high but not to panic because of how many false positives there are when looking inside someone’s body.

While I am happy to report they didn’t find anything serious, I do take slight offense to the following at the top of my results:

Last name, First name: Unremarkable

(Kidding of course but still got a chuckle out of me)

by sharkweek

2/14/2026 at 9:51:22 PM

Anecdotal evidence to confirm: I had two false alarms from an unrelated MRI scan, and beside wasting a lot of time on diagnosing them - it was also extremely stressful.

My father is a part of "full body PET scan every 3 years" program as part of post - cancer treatment, and it worked twice: early detected lung and prostate tumors, both removed.

by rembal

2/14/2026 at 9:59:49 PM

> My father is a part of "full body PET scan every 3 years" program as part of post - cancer treatment,

These treatments are wonderful and it is great that they exist. But many people fail to understand the difference in terms of pretest probability, etc.

I can absolutely see the heavy psychological impact pending biopsy results may have. People are quick to discount these issues when you raise them as a concern, but only if they never went through this stress themselves

by p0pularopinion

2/14/2026 at 10:15:31 PM

I have multiple scans a year. "Scanxiety" is real.

by mcbain

2/14/2026 at 10:25:39 PM

hmm that is still around 1.5% of ppl having cancer. not trivial. Even more if you include false negatives.

by paulpauper

2/14/2026 at 10:43:58 PM

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by NedF

2/14/2026 at 10:16:21 PM

And yes getting frequent full body MRIs is still overwhelming the right thing for the patient.

by mgraczyk

2/14/2026 at 10:18:09 PM

No? The point of the article, and of the preceding comments, echoing a pretty common tenet of evidence-based medicine, is that frequent full-body MRIs are a bad idea for the patient.

by tptacek

2/14/2026 at 9:07:56 PM

Answering the question in the title...

> One study in 2020 found that 95% of asymptomatic patients had some type of "abnormal" finding, but just 1.8% of these findings were indeed cancer.

So a bit less than 1.8% of the time in this study

> Prenuvo's recent Polaris Study followed 1,011 patients for at least one year following a whole-body MRI scan. Of these patients, 41 had biopsies. More than half of the 41 were diagnosed with cancer.

That's 2.0%

Note that this doesn't mean that 1.7~2.0% of people have cancer without knowing it. It could be more:

> A negative scan doesn’t mean you’re disease-free. Some cancers and conditions simply aren’t visible yet or aren’t reliably detected on a one-time full-body MRI."

But also perhaps less, in a way:

> "You're finding something that never would have caused you any problem in your life, and in cancer, we call that overdiagnosis," Vickers says.

by lucb1e

2/14/2026 at 9:24:33 PM

Yep, I have experience with both. It found cancer for my wife and she was able to treat it immediately. Fully recovered.

It found a weird spot on me that turned out to a pancreatic rest.

The only reason we did the scans were because we were making a significant life decision that we didn’t want to have to backtrack if either got diagnosed with cancer within a year . We knew nothing was guaranteed but we wanted to do some tests.

by jml78

2/14/2026 at 9:31:13 PM

> You're finding something that never would have caused you any problem in your life

Is it though? Isn't it possible you could be early-detecting something serious that is much easier to treat now vs when symptoms appear?

by majorchord

2/14/2026 at 10:04:35 PM

Yes, you could early-detect something, but the likelihood of this thing being life-threatening are extremely low. If you choose to manage this thing aggressively anyway, you have to undergo more invasive testing (e.g., biopsies, surgery, anesthesia, etc.) that all have small risks of catastrophic events. In most cases, the risks of more invasive testing outweigh the risks of just not pursuing any further workup.

Nothing in medicine comes for free—everything is a tradeoff.

by sxg

2/14/2026 at 9:55:38 PM

> Isn't it possible you could be early-detecting something serious that is much easier to treat now vs when symptoms appear?

It could be. It could also be the cade that you undergo invasive surgery for something that would have never caused you problems within your life. The problem is that cancer isn‘t cancer. Even if it originates from the same tissue, some tumors behave very different from others.

by p0pularopinion

2/14/2026 at 10:28:05 PM

Yeah a 2% risk of having something which can easily kill you and is very expensive to treat, especially if you're not elderly and still have lots of life ahead of your, is not exactly trivial. I would want to know about this

by paulpauper

2/14/2026 at 10:36:05 PM

One important point is that many people die WITH cancer but not OF cancer. So even for the 1.8%, only a fraction of those people were going to die of the disease (or even suffer significant symptoms) - the rest were just going to die of natural causes anyway.

But now you've found it you pretty much have to remove it, which has significant quality of life implications.

by jamesbelchamber

2/14/2026 at 10:43:20 PM

This seems like a wild statement.

Age is a big factor in the with/of cancer factor. If someone is 80 years old then there's good chance it won't be cancer that kills them (assuming they aren't already in a late stage).

But if you are 40 and you have cancer, there's a good chance you'll die of that cancer if it's left untreated.

I'm personally of the opinion that cancer screening should happen earlier for younger people and less frequently for older people. Like, if you hit 80, there's really basically no reason to screen for cancer.

by cogman10

2/14/2026 at 10:03:33 PM

Just to point out, cancer isn't the only reason to get these. Aneurisms, hemachromatosis, etc can all be serious. I know someone who got scanned for $500 and they caught hemachromatosis via iron deposits in the liver. Much better than eventual chirrosis and liver failure.

by giantg2

2/14/2026 at 10:20:21 PM

What's the base rate of hemachromatosis in the population and what's the false positive rate for MRI detection of the condition?

by tptacek

2/14/2026 at 10:31:09 PM

MRI does not diagnose hemachromatosis. It detects iron deposits (could be due to other harmful issues). To my knowledge it would not produce a false positive. Hemachromatosis is the most common genetic issue in white people, so pretty common (I'm too lazy to look up stats).

by giantg2

2/14/2026 at 9:31:25 PM

Maybe the right answer isn't to do a biopsy, but to monitor the area with follow-up scans? It seems like that addresses much of the harm that a false positive can cause (invasive biopsy leading to complications) while maintaining most of the gains (still very early detection).

by jmward01

2/14/2026 at 10:01:22 PM

The problem is that just because you‘re detecting something, it does not mean it is worth watching. Bodies are not standardized and most people habe something off. But you can‘t really reschedule everybody constantly, as that would entirely break the concept.

by p0pularopinion

2/14/2026 at 10:11:11 PM

"Worth watching" implies that watching is expensive. It's really not. A full-body MRI scan is about $1k, and it can be even cheaper.

So if you have abnormal findings in 10% of patients that merit follow-up scans, you can trivially do a series of 3-4 scans without affecting the overall cost too much.

Doctors simply need to get out of the headspace where MRIs are extremely scarce tools of last resort and treat them like we treat blood tests.

by cyberax

2/14/2026 at 10:38:34 PM

I totally agree. US healthcare is broken and costs aren't tied to the reality of how expensive something actually is. I have very high hopes that modern medicine is in for a massive disruptive change where things like full body MRI, along with analysis, could be done very cheap and with no admin overhead. In that model 'we see something we aren't sure of. It is probably nothing but to be sure we want to do follow-ups' is far less of a problem.

A lot of this however is how it is discussed with the patient. Discussions about the likelihood of there being a real issue when something is seen need to be clear and informative without being alarming. 'We did a routine scan and these often show transient artifacts that turn out to be nothing, but in an abundance of caution we want to do a followup' is totally different than 'we saw something we are concerned about and need to do a followup'. How things are messaged really matters.

by jmward01

2/14/2026 at 10:22:12 PM

I think you're missing the point. The psychological cost of a conditional-positive result is nonzero, and can be very significant (I speak from a little bit of experience here). But far more importantly: the physiological cost of invasive followups when you eventually trip the threshold of "time to go explore with a scalpel" is very high, and the missing evidence this story is about is whether you can get to that threshold with an MRI.

Treating MRIs the way we treat blood tests would almost certainly result in huge numbers of needless invasive procedures.

by tptacek

2/14/2026 at 10:20:51 PM

Doctors here are cognitively captured by a system designed to limit cost (and that's mostly a good thing)

But scanning frequently is overwhelmingly good for the patient. The problem is the doctors. Imagine two possibilities. 1. You scan every six months and a doctor reviews your scans but never tells you anything no matter what 2. You scan every six months and a doctor reviews your scans and only tells you results if you have an obviously growing mass that has a probability greater than 95% of being cancerous

Obviously #2 is better for the patient than #1, but #1 is equivalent to never testing if you ignore cost.

So the actual reason we don't have effect frequent scans combined with effective diagnostic techniques is cost, and doctors cope with this reality by saying clearly wrong things about "over diagnosis". It's a local minimum of the payer/provider dynamic that has nothing to do with scans per se.

by mgraczyk

2/14/2026 at 9:11:54 PM

I pay an extra $60 a year to have my ophthalmologist take a digital image of my retina. It comes back as normal every year, but if something does change we can diff the image against the baseline.

Maybe I don't want to look for cancer right now but if I spend $1,000 every 5 years to take an image for later use... isn't that useful?

by joezydeco

2/14/2026 at 9:38:43 PM

Might be, but in the context it's also worth asking what better options you have for your health with that $1000.

(for some people that question may not apply, of course, but at a population level it does, and we have population-level questions about effective use of MRI time.). And if there's something better, you should spend it on that and then ask the question _again_. So it could be that getting a whole-body MRI is something like $30k down the list of best ways to spend money for improved health.

I'm not sure what the best use of $1k is from a health standpoint is, just noting that it's good to have a comparator.

by dgacmu

2/14/2026 at 9:29:44 PM

Yes, and it seems like its purposefully ignored in the "body scan" debate. full CT scans would be more problematic, and MRI's (especially no contrast ones) don't pick up a lot of things... but having annual comparisons over a few years would likely fill in some of those gaps. literally and figuratively.

by butvacuum

2/14/2026 at 9:17:08 PM

Er wait is retinal cancer a thing?

by johndhi

2/14/2026 at 9:27:08 PM

Yes. Like OP, I do a picture every year. Three years ago there was a scare, that turned out to be nothing.

by lbreakjai

2/14/2026 at 10:02:50 PM

Yes. You can also have melanoma on your uvea

by p0pularopinion

2/14/2026 at 9:30:21 PM

theres a ton of degeneative stuff too that's not strongly age corrilated.

by butvacuum

2/14/2026 at 9:25:01 PM

1. collecting baseline info for later comparison is good

2. i can afford the money for the chance of early detection. Many cancers are symptomatic only in the latter stages. It does not hurt to check.

by dmitrygr

2/14/2026 at 9:35:59 PM

There’s a major difference between having insurance cover something (socialized cost, immediately drives up provider fees for bizarre reasons) and letting the market allow people to buy it themselves (individual cost, the market drives the cost down fast and hard). Notice the pattern with LASIK and GLP1 where lack of insurance coverage has counterintuitively made it cheaper and more accessible.

Let everyone who wants to pay get their scans! But don’t make me pay for you

by monero-xmr

2/14/2026 at 10:37:31 PM

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by NedF