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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?

#161

Post by bonsai_spool »

RobotToaster wrote: post #159
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…

>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.

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

#162

Post by M95D »

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.

If the cancer is vizible in MRI or CT scans, the immune system already failed to "resolve" it and will not do so in the future, at least not without external help.

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

#163

Post by armada651 »

RobotToaster wrote: post #159
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…

>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.

I wonder how biased the group is though, is the sample truly representative of the general population or is it a group of people who are already undergoing screen for some other health-related reason?

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

#164

Post by pfdietz »

rustyhancock wrote: post #125
ErroneousBosh wrote: post #122

Earlier quoted context omitted.

> The danger of an unnecessary CT/PET is causing cancer You'd have to be massively overexposed to CT or PET scanning to cause cancer, like in the region of spending months being scanned continuously with it at full beam current.

Even if you don't agree with linear no threshold models for cancers induced by radiation (I don't think LNT is accurate). It comes down to the scan and the age. 3 scans for a 1 year old? Strongly associated with cancers later in life. 5 scans of a 50 year old? Less so. The 1 year old has an 80 year run way to develop cancer, along with cells already set in a state of rapid division, and a less developed immune system…

> I don't think LNT is accurate

There's excellent reason to think LNT is accurate: at low doses, almost every cell is exposed to at most one radiation event. The dose affects how many cells experience a (single) event, but does not affect the level of damage to those exposed cells. Linearity naturally falls out of this.

To abandon linearity you have to imagine some sort of signalling system (not observed) that kicks in at just the dose we're talking about (not lower, not higher) to allow exposure to one cell to affect other cells.

There's also no good evidence that LNT is wrong. The typical things that are pointed to by anti-LNT cranks are cherrypicked, often involving interim results from studies the full results from which do support LNT, which is evidence it was statistical noise.

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

#165

Post by gjulianm »

RobotToaster wrote: post #159
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…

>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.

The argument for better screening would require that finding those asymptomatic cancers actually improves survival rates. There are several reasonable scenarios where early screening doesn't improve it:

* The cancer is aggressive and resistant to treatment. Chemo/radiation only pause the growth for a bit, but ultimately the cancer keeps growing and the total survival time is the same (only that the patient spent more time knowing they had cancer).

* The cancer is susceptible enough to treatment that it's still curable when it becomes symptomatic and found through other means.

* The cancer is slow enough that the patient dies from other causes before.

Early screening brings benefits only when the cancer ends up causing issues and responds differently to treatment between the "early screening detection" time and the "normal detection" time.

It's impossible to know beforehand which of the scenarios have more weight, specially because we have very little data on what happens way before cancer is detected via the usual methods. We need better studies on this, and for now the evidence doesn't really point out to these large, indiscriminate screenings being actually helpful.

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

#166

Post by ErroneousBosh »

lostlogin wrote: post #127
ErroneousBosh wrote: post #122

Earlier quoted context omitted.

> The danger of an unnecessary CT/PET is causing cancer You'd have to be massively overexposed to CT or PET scanning to cause cancer, like in the region of spending months being scanned continuously with it at full beam current.

> You'd have to be massively overexposed to CT or PET scanning to cause cancer The mean effective dose for all patients from a single PET/CT scan was 20.6 mSv. For males aged 40 y, a single PET/CT scan is associated with a LAR of cancer incidence of 0.169%. This risk increased to 0.85% if an annual surveillance protocol for 5 y was performed. For female patients aged 40 y, the LAR of cancer mortality increased from 0…

> 0.126 to 0.63%

So, a just-about-measurable increase, if you pick and choose your values carefully?

You are not going to die from cancer caused by getting a PET scan. This will not happen.

You're going to die of heart disease or as a not-too-distant second in a car accident.

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

#167

Post by ErroneousBosh »

azan_ wrote: post #138
ErroneousBosh wrote: post #122

Earlier quoted context omitted.

> The danger of an unnecessary CT/PET is causing cancer You'd have to be massively overexposed to CT or PET scanning to cause cancer, like in the region of spending months being scanned continuously with it at full beam current.

Approx. 5% of all cancers in US are caused by CTs

[citation needed]

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

#168

Post by pfdietz »

MagicMoonlight wrote: post #144
srean wrote: post #136

Earlier quoted context omitted.

False positives trigger more diagnostics some of which can be harmful, not just psychologically but physiologically as well. If false positives are ok, why not build a down time detector that rolls a die every 5 mins and alert on hitting a 6.

Harmful to shareholder value. Personally I’d rather have cancer checked out rather than have a “wait and die” approach

Insurance-based medical systems mean the patient has transferred responsibility for saying no to those actually paying the bills. They have to draw the line somewhere.

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

#169

Post by gjulianm »

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…

> 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.

Why is it likely? We already have a lot of MRI data. There are already a lot of incidental findings. It might also be an issue of the MRI not being able to produce enough information to discriminate.

> To use a software analogy, if your downtime detection system kept producing false negatives, would your solution to be just turn it off? You'd get some better night's sleep, but you'd pay for it when the system really went down and you had no idea.

The analogy is rather something like this: your downtime detector is not just a "ping" but a full web browser that tests everything and it sometimes flags things that are not actually issues. So you don't turn it off, but you only use it when you have another signal that indicates that something might be going wrong.

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

#170

Post by pfdietz »

I much prefer tests with low false positive rates.

I recently had such a cancer-related test. A cousin had a BRCA2 mutation and I was concerned I could have it also. Insurance would not pay for the testing, but one can get a panel of such genetic tests for just $250 now, so I went ahead. And it was negative. This is reassuring not just to me, but also to my children, and (somewhat) my sibling (the relevant parent is no longer alive).

Had this test been positive, the chance of pancreatic cancer would have gone way up, so frequent scans (I think annual MRI and ultrasound?) would have been justified.

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