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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?

#231

Post by gjulianm »

IshKebab wrote: post #226
gjulianm wrote: post #173

Earlier quoted context omitted.

> This is much more sensible than just not testing at all and letting people die from cancer. This is not what happens. You're assuming that if the cancer does not get detected by the screening then it never gets detected. What actually happens is that the test gives information that might actually be redundant and obtainable in less risky way. What the studies are showing is that waiting until there are other, more…

Interesting. Do you have a source for that?

See https://pubmed.ncbi.nlm.nih.gov/38926075/. I was not aware of the ERSPC which came out late last year and gives better outcomes for screening, but overall the evidence is not super clear yet. There are possibly certain groups that can benefit from PSA screening more than others. Also, modern, more effective treatments might allow for later diagnosis with the same clinical results.

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

#232

Post by gjulianm »

IshKebab wrote: post #175
gjulianm wrote: post #172

Earlier quoted context omitted.

> If the test detects cancer that doesn't need treatment, don't treat it!! How do you know which ones to treat and which ones to leave?

When the result is above a chosen threshold (which may depend on other factors like family history etc.).

Unfortunately that "chosen threshold" is really hard to know, specially if you want to balance individual and population level necessities.

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

#233

Post by gjulianm »

danw1979 wrote: post #227
_alternator_ wrote: post #208

Earlier quoted context omitted.

The major reason not to do this is that you often get worse outcomes for patients. Oncology provides a lot of examples where “more knowledge” does not lead to better outcomes. Routine ovarian cancer screening, prostate screens, childhood neuronlastoma screens, and breast cancer screens all have shown that overuse will identify more cancer, but do not lead to better outcomes like reduced mortality. The reasons are com…

I’m married to someone running various prostate cancer studies in the UK. I hear the arguments against screening a lot and the issue really blew up recently in the news here. The thing is, when researchers talk about “worse outcomes” they’re often comparing survival (or rather lack of) against terrible side-effects. What this fails entirely to capture is that doing something to increase your odds of survival, damn th…

> What this fails entirely to capture is that doing something to increase your odds of survival, damn the consequences, is an individual choice.

What you're failing to capture is that this is a hard problem because it's both an individual choice and a collective one as well. Those "terrible side effects" might actually end up killing someone. You're choosing between a high-chance lottery on a small population or a low chance lottery on a far larger one. It's not that simple.

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

#234

Post by tptacek »

cyberax wrote: post #84
tptacek wrote: post #31

Earlier quoted context omitted.

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 thr…

> Treating MRIs the way we treat blood tests would almost certainly result in huge numbers of needless invasive procedures. Again, _all_ you need to do is to make a follow-up scan in 1-3 months to see if there are any changes. It's a preventative tool, so unless you have other indications, it's almost always safe to wait for a bit. And yes, it requires educating patients that sometimes just waiting and doing a follow…

* Doctors and medical researchers keep saying that routine MRIs for non-symptomatic or low-risk patients is a bad idea, because the outcomes are worse than not scanning.

* There's several clear, understandable mechanistic reasons why this would be the case, including simple applications of the base rate fallacy.

* Nevertheless, here we are, nerds arguing we know better than all these people.

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

#235

Post by RobotToaster »

bonsai_spool wrote: post #161
RobotToaster wrote: post #159

Earlier quoted context omitted.

>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. That can also be reframed as 1.71% of asymptomatic people having cancer, which is a really good argument for better screening.

That’s not the correct framing - your assertion first lacks evidence about why we should screen better. In fact, we aren’t improving longevity in many early diagnoses, and may be treating people whose immune system would resolve the cancers. Further, the denominator is asymptomatic people who were able to get MRI’s they didn’t need . That doesn’t tell us anything about the normal world.

> we aren’t improving longevity in many early diagnoses, and may be treating people whose immune system would resolve the cancers.

Even assuming your statement is true, if what is detected is small enough for that there's no reason "treatment" can't just be monitoring it's size with follow-up scans.

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

#236

Post by tptacek »

mgraczyk wrote: post #95
Snoozus wrote: post #94

Earlier quoted context omitted.

No, you still wouldn't, because doctors are neither free nor perfectly rational. The probability of finding something worth a biopsy is not low, it is high compared to the probability of the patient requiring intervention.

Yes that is my point. It's about cost

That's not what they said.

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

#237

Post by mgraczyk »

RataNova wrote: post #153
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…

I don't think this is doctors being captured by the system so much as medicine being cautious about scaling interventions without strong outcome data

Nope, this is cope

Tons of diagnostic interventions have been scaled without strong outcome data. For example many clinics now do fractional exhaled nitric oxide (FeNO) tests because they are safe, fairly cheap, and patients often pay directly out of pocket so they are easy to make money on.

But the evidence for the diagnostic usefulness of this test is extremely low, multiple meta analysis have concluded.

The reason FeNO tests are done but not MRIs is because FeNO tests are $40

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

#238

Post by mgraczyk »

alexey-salmin wrote: post #123
mgraczyk wrote: post #107

Earlier quoted context omitted.

> 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

No, the detector doesn't fix that, that problem is not treating people without cancer. The problem is treating people with cancer that won't kill or harm them during their lifetime. In this case even a low risk treatment becomes harmful, let alone cancer treatments.

Your claim is equivalent to claiming that most cancer treatment is net harmful btw

and this is obviously false, especially for cancers detected earlier

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

#239

Post by masterlee_fn »

n8henrie wrote: post #196
kcexn wrote: post #135

Earlier quoted context omitted.

There's a softer component to healthcare which is that people can overreact to medical results. If a doctor administers a scan, finds a handful of likely benign things but wants to administer another scan later on down the line, I'm probably much more likely to look for a second opinion that tells me to cut them out (even if it may not be medically necessary) than trust my doctor that "it's probably fine". It's proba…

Not to mention the malpractice risk and potential for extra income, which -- depending on where you live -- may strongly (if subconsciously) influence your physicians interpretations and recommendations. Do you think a doctor is more likely to call something "possible cancer" and recommend that you either have a specialist do a biopsy (keeping in mind that many of these will be... hard to reach) or at least have a fo…

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

#240

Post by masterlee_fn »

_alternator_ wrote: post #208
nayroclade wrote: post #129

Arguments against proactive MRI scanning always seem to have a whiff of status quo bias to them. Yes, right now MRIs are expensive and false positives are common, but if regular scans were widespread, it's likely this result in innovations that would drive down costs, improve accuracy, as well as producing a much larger corpus of data with which to guide diagnosis and reduce false positives. To use a software analogy…

The major reason not to do this is that you often get worse outcomes for patients. Oncology provides a lot of examples where “more knowledge” does not lead to better outcomes. Routine ovarian cancer screening, prostate screens, childhood neuronlastoma screens, and breast cancer screens all have shown that overuse will identify more cancer, but do not lead to better outcomes like reduced mortality. The reasons are com…

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