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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?

#51

Post by mgraczyk »

lich_king wrote: post #50
mgraczyk wrote: post #29

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…

Why is it good for the patient? I think that to claim this, you'd need to show a difference in outcomes. Here, you have a tool with a ~100% false positive rate, so if we start administering it to everyone, it will almost certainly cost lives. Botched biopsies, unnecessary treatments, other complications. Not to mention the huge cost that would divert money from other welfare programs. So you need to show that when it…

Did you read my two options? Do you agree option 2 is better than option 1? If so, then scans are better than no scan

You don't need to show that it's possible to avoid false positives. That's doctors being irrational.

You only need to show that it's possible to build a diagnostic system that's better than no testing, and I have shown that already

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

#53

Post by rustyhancock »

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…

It's not that MRIs suck at cancer. They provide fantastic structural and functional data.

The problem is the specificity of the results and the prior.

A full body MRI by definition will provide detailed views of areas where the pretest probability for cancer is negligible. That means even a specific test would result in a high risk of false positives.

As a counter point, MRS means that you can now MRI someone's prostate and do NMR on lesions you find.

Lets say someone has lower urinary tract symptoms. And is 60 years old. An MRI could visualize as well as do a analysis that would otherwise require a biopsy. With the raised prior you can be quite sure suspicious lesions are cancerous.

Similarly for CNS tumours. Where fine detail. Subtle diffusion defects can mark csncers you couldn't even see if you cut the person open.

No sensible doctor would give you a whole body CT unless there was a very good reason. That very good reason is probably "we already think you have disseminated cancer". That pushes the prior up.

And less so for a PET/CT. Lets flood you with x-rays and add some beta radiation and gamma to boot!

The danger of an unnecessary CT/PET is causing cancer, the danger of an unnecessary MRI chasing non existent cancer.

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

#54

Post by [deleted] »

mcbain wrote: post #23
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…

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).

[deleted]

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

#55

Post by skywalqer »

mgraczyk wrote: post #29

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…

Best comment here

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

#56

Post by mmaunder »

mgraczyk wrote: post #25
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…

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

This guy has never heard the term 'scanxiety'. Go ask what it means on a cancer forum. The real OG's are the VHL folks. Bet we have a few here on this thread. Respect.

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

#57

Post by lich_king »

mgraczyk wrote: post #51
lich_king wrote: post #50

Earlier quoted context omitted.

Why is it good for the patient? I think that to claim this, you'd need to show a difference in outcomes. Here, you have a tool with a ~100% false positive rate, so if we start administering it to everyone, it will almost certainly cost lives. Botched biopsies, unnecessary treatments, other complications. Not to mention the huge cost that would divert money from other welfare programs. So you need to show that when it…

Did you read my two options? Do you agree option 2 is better than option 1? If so, then scans are better than no scan You don't need to show that it's possible to avoid false positives. That's doctors being irrational. You only need to show that it's possible to build a diagnostic system that's better than no testing, and I have shown that already

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 an unusual place. Or it may be slow-growing prostate cancer that you can live with for another 20 years, and maybe it's the chemotherapy that will do you in. It's really not that clear-cut in medicine.

To give you have another example: let's say that the risk of appendicitis in people who have an appendix is 1%. And the risk in people who had an appendix removed is 0%. Does this justify proactively removing the appendix? No, because the consequences of complications are much higher than the harm you're preventing. The same applies here: detection, even if 100% accurate, doesn't mean anything. You need to show that what you do with the result actually helps.

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

#58

Post by mgraczyk »

mmaunder wrote: post #56
mgraczyk wrote: post #25

Earlier quoted context omitted.

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

This guy has never heard the term 'scanxiety'. Go ask what it means on a cancer forum. The real OG's are the VHL folks. Bet we have a few here on this thread. Respect.

I have, it's the fault of how medicine is practiced to reduce cost. It's completely avoidable, you can just not tell people their scan results if they have no symptoms and the detection is less than 95% likely to be cancer. This is strictly better than the status quo because the only difference is some people who almost certainly have cancer learn that they have cancer and nothing else changes

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

#59

Post by mgraczyk »

lich_king wrote: post #57
mgraczyk wrote: post #51

Earlier quoted context omitted.

Did you read my two options? Do you agree option 2 is better than option 1? If so, then scans are better than no scan You don't need to show that it's possible to avoid false positives. That's doctors being irrational. You only need to show that it's possible to build a diagnostic system that's better than no testing, and I have shown that already

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 longer make a difference whether you treat it or not. Or it may be that you would have lived another 20 years just fine

This is just wrong for many parts of the body. In your brain? Your lungs? Growing for a year between 3 scans 6 months apart? Extremely unlikely to be benign

> The same applies here: detection, even if 100% accurate, doesn't mean anything. You need to show that what you do with the result actually helps.

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

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

#60

Post by tptacek »

mgraczyk wrote: post #58
mmaunder wrote: post #56

Earlier quoted context omitted.

This guy has never heard the term 'scanxiety'. Go ask what it means on a cancer forum. The real OG's are the VHL folks. Bet we have a few here on this thread. Respect.

I have, it's the fault of how medicine is practiced to reduce cost. It's completely avoidable, you can just not tell people their scan results if they have no symptoms and the detection is less than 95% likely to be cancer. This is strictly better than the status quo because the only difference is some people who almost certainly have cancer learn that they have cancer and nothing else changes

Again, you're assuming the only downside of a routine scan is anxiety. No, the real downside is that you'll trigger needless invasive procedures.
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