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How often do full-body MRIs find cancer?

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Re: How often do full-body MRIs find cancer?

#101

Post by foota »

rich_sasha wrote: post #98

Can someone ELI5 why false positives on a MRI are so bad? From a pure Bayesian PoV, you're better off with a noisy additional observation. At worst it doesn't get much weight. At a pragmatic level, can't you say, hey here's something thats probably nothing, let's scan it again in 6 months? Why does an MRI necessarily lead to invasive follow ups? I get that ideally we'd have a crystal ball with 0 type I / type II erro…

My understanding is it's liability, if the doctor decides not to look into it then they could be blamed for it if it turns to cancer.

Re: How often do full-body MRIs find cancer?

#102

Post by alexey-salmin »

majorchord wrote: post #10
lucb1e wrote: post #2

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 diag…

> 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?

There's a theory that the first-stage cancer is way more common than we think, it's just doesn't develop further most of the time, cause no symptoms and remains undiagnosed throughout the lifetime.

There's some support for this view because agressive screening for thyroid and prostate cancers increases the number of surgeries a lot but doesn't seem affect the mortality rates.

Risks from a surgery are non-negligible, if you perform it to treat a low-risk condition it may be a net loss in the end.

So you're technically right about the "early-detecting" part, but the "much easier to treat" step is problematic because it's unclear what a net-positive treatment looks like for low-risk cases. Probably it comes down to yearly monitoring of whatever was detected, not the actual treatment.

Re: How often do full-body MRIs find cancer?

#103

Post by graboy »

mgraczyk wrote: post #86
lostlogin wrote: post #85

Earlier quoted context omitted.

… they do it based on the scan result. Avoiding a biopsy that wasn’t needed is a good thing.

You're imagining that the doctor is required to act irrationally or against the patient's interest. I understand that they do act this way, but I'm pointing out that they don't have to! You walk into a doctor's office and meet for the first time. Case 1. You have 3 full body MRIs taken 6 months apart in hand and give them to your doctor. Nobody has opened or looked at the scans yet. Case 2. You do not have a scan yet…

I kinda agree with you and I understand your point but I also think there is a social-ethical reality that if a doctor finds something they must treat it. The two options are 1. doing nothing, or 2. reducing cancer risk and you get unnecessary biopsies.

You're thinking of this as there being an objective positive utility for not dying of cancer and a objective negative utility for biopsies, and there being an objective optimal "rational" tradeoff that the best radiologist can optimize for to get their "nearly certain" detection threshold.

But frankly - the tradeoff for the value of a human life is perhaps the most uncertain thing one could choose. It lies in the eyes of the patient if the worry and time associated with a false detection is worth their reduced chance of death. The ethical uncertainty expressed in the OP - are these unnecessary biopsies worth it - is warranted.

Re: How often do full-body MRIs find cancer?

#104

Post by alexey-salmin »

mgraczyk wrote: post #59
lich_king wrote: post #57

Earlier quoted context omitted.

No. To argue for the benefit of the procedure, you need to show a difference in outcomes. Not that it can detect something, even if it could (which whole-body MRIs clearly don't). That the detection improves your chances of survival. If you have an growing mass in your body, then if it's cancer, after a year, it might be too late for treatment. Or it may turn out to be nothing: a benign tumor / cyst / fat deposit in…

The difference in out come is With my change: 95% of people who are shown scans have cancer and are treated earlier. 5% of people do not have cancer and get CT scans. 0.5% of people get useless biopsies Without my change: many of those 95% die, the 0.5% do not get useless biopsies And the beauty of this is you can pick the percentage! > If you have an growing mass in your body, then after a year, it may very well no…

> With my change: 95% of people who are shown scans have cancer and are treated earlier. 5% of people do not have cancer and get CT scans. 0.5% of people get useless biopsies Without my change: many of those 95% die, the 0.5% do not get useless biopsies

You assume that treating cancer automatically improves the outcome. Treating cancer often kills you, so treating a non-fatal tumor can easily be a bad decision. And a lot of the tumors found by agressive scans are like that, but we don't know yet how much exactly and how to tell one from the other. It's a new question that requires decades-long observations to answer.

> This is wrong. If you had a 100% accurate cancer detector, fewer people would die of cancer with no downside

You're saying it as if detection somehow cures cancer, it doesn't.

Re: How often do full-body MRIs find cancer?

#105

Post by matwood »

mmaunder wrote: post #13

“ 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 ve…

> MRIs are great for certain things like herniated disks in your back.

I have had a lot of experience with MRIs on both myself (back and knee [1]) and my dogs with herniated discs. The doctors always make it sound like MRIs are great to confirm what's suspected because of other symptoms like pain, but a point in time MRI alone is not that valuable. Everyone's bodies (including animals!) are surprisingly different inside making normal be somewhat unique. I think what would be interesting is if scanning technology like MRIs could be made so inexpensive and easy that everyone had one done 4x/year. That way it's the differential being checked and I'm guessing it would be way more valuable. Normalization such as this could also lower anxiety around findings.

[1] Even when I tore my ACL the MRI came back only as probable.

Re: How often do full-body MRIs find cancer?

#106

Post by mapt »

lostlogin wrote: post #76
giantg2 wrote: post #20

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.

A blood test is a far cheaper way to check this.

No it isn't.

If you get the MRI you are performing simultaneous blind tests for a thousand rare, unsuspected conditions. The blood test only tests for one of them, and eats 10ml of blood. There isn't enough blood in your body for all those tests.

We should arguably be, in an ideal healthcare system, getting annual MRIs with the other typical tests in a physical, and feeding that data into an AI, and have the AI issue recommendations for informed hazard & secondary testing/biopsy priorities. Tomographic analysis and differential diagnosis is exactly the sort of multidimensional pattern recognition task an AI is great at compared to a human doctor, if you can provide the training data.

Normalizing an annual MRI is the biomedical equivalent to survey astronomy and opening up those gargantuan datasets - you expect lots of simultaneous serendipitous discoveries in unrelated areas without securing an organizational mandate to fund a dedicated research effort into each one of them. The worst the process is ever going to be diagnostically is right now before we're collecting any data in a concerted fashion - every bit of training improves it.

Re: How often do full-body MRIs find cancer?

#107

Post by mgraczyk »

alexey-salmin wrote: post #104
mgraczyk wrote: post #59

Earlier quoted context omitted.

The difference in out come is With my change: 95% of people who are shown scans have cancer and are treated earlier. 5% of people do not have cancer and get CT scans. 0.5% of people get useless biopsies Without my change: many of those 95% die, the 0.5% do not get useless biopsies And the beauty of this is you can pick the percentage! > If you have an growing mass in your body, then after a year, it may very well no…

> With my change: 95% of people who are shown scans have cancer and are treated earlier. 5% of people do not have cancer and get CT scans. 0.5% of people get useless biopsies Without my change: many of those 95% die, the 0.5% do not get useless biopsies You assume that treating cancer automatically improves the outcome. Treating cancer often kills you, so treating a non-fatal tumor can easily be a bad decision. And a…

> You're saying it as if detection somehow cures cancer, it doesn't.

No, I didn't say the detector would cause cancer to be cured. I said fewer people would die with no downsides. If treatment is sometimes harmful then the detector also fixes that, you'd never treat people without cancer

Re: How often do full-body MRIs find cancer?

#108

Post by throwup238 »

_heimdall wrote: post #89
gullywhumper wrote: post #68

Earlier quoted context omitted.

2.5 years in of regular PET scans. At this point, I’m almost humored by what gets flagged as suspicious by the radiologist - usually mosquito bites and stomach bugs (kids in daycare means I’m almost always sick). I have a scan Monday and two weeks ago had a re-excision so there’s a two inch gash healing on my back. This week I got three vaccines. And then tonight my toddler bit me hard enough to draw blood. I had ask…

How often are they finding actual positive hits on the PET? If its so unreliably with regards to false positives why do you continue to have PET scans done?

PET scans are not really unreliable, they’re just very sensitive and lots of anomalies ranging from benign cysts to malignant tumors show up on them. It’s not always possible to differentiate them without other measures like biopsies, so that’s where the false positives come in.

Getting regular scans to track cancer progression is a different matter altogether, since most of the blips can be eliminated over time and there’s a history to compare against.

Re: How often do full-body MRIs find cancer?

#109

Post by maho »

rich_sasha wrote: post #98

Can someone ELI5 why false positives on a MRI are so bad? From a pure Bayesian PoV, you're better off with a noisy additional observation. At worst it doesn't get much weight. At a pragmatic level, can't you say, hey here's something thats probably nothing, let's scan it again in 6 months? Why does an MRI necessarily lead to invasive follow ups? I get that ideally we'd have a crystal ball with 0 type I / type II erro…

> At a pragmatic level, can't you say, hey here's something thats probably nothing, let's scan it again in 6 months

If a doctor even _hints_ there might be cancer, the patient will have a terrible 6 months (with actual, measurable negative health impacts of the added stress). Also, at some uncertainy-level (say, 10% chance of cancer) the doctor _has_ to say something and has to schedule expensive followups to not risk liability, even though in 90% of the cases it is not only unnecessary, but actively harmful to the patients.

When, on average, the cost of the screening + the harm done by a false positive outweighs the benefits of an early detection, you shouldn't do the screening in the first place.

Re: How often do full-body MRIs find cancer?

#110

Post by lostlogin »

mapt wrote: post #106
lostlogin wrote: post #76

Earlier quoted context omitted.

A blood test is a far cheaper way to check this.

No it isn't. If you get the MRI you are performing simultaneous blind tests for a thousand rare, unsuspected conditions. The blood test only tests for one of them, and eats 10ml of blood. There isn't enough blood in your body for all those tests. We should arguably be, in an ideal healthcare system, getting annual MRIs with the other typical tests in a physical, and feeding that data into an AI, and have the AI issue…

> The blood test only tests for one of them, and eats 10ml of blood. There isn't enough blood in your body for all those tests.

There is some irony here. Getting some blood out is what will cure that iron overload.

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