Comment by mmaunder
5 days ago
“ 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.
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.
> Lets say someone has lower urinary tract symptoms. And is 60 years old. An MRI could visualize as well as ...
Not a doctor - but maybe start with some quick & cheap tests of their blood & urine, polite questions about their sexual partners, and possibly an ultrasound peek at things?
At least in America, high-tech scans are treated as a cash cow. And cheap & reasonable tests, if done, are merely an afterthought - after the patient has been milked for all the scan-bucks that their insurance will pay out.
Source: Bitter personal experience.
> At least in America, high-tech scans are treated as a cash cow. And cheap & reasonable tests, if done, are merely an afterthought - after the patient has been milked for all the scan-bucks that their insurance will pay out.
Maybe it's a regional thing, but that hasn't been my experience. I've had one MRI and one CT scan in the 25+ years that I've been a full-time employed adult with insurance.
I'd have been happy to sign up for more so I could have proactive health information and the raw data to use for hobby projects.
> 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.
But the association is quite strong.
https://www.sciencedirect.com/science/article/pii/S0720048X2...
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> 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 0.126 to 0.63% if an annual surveillance protocol for 5 y was performed.
https://pubmed.ncbi.nlm.nih.gov/36856709/
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Approx. 5% of all cancers in US are caused by CTs
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> 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.
Do you know which MRI you used? Not all are equal. Most MRI are 1.5T powered, and you can’t get fine details until you hit 3T. And there are differences even in the 3T power range. There are higher powered MRI which are mostly only used in research, whilst it is a bit scary thinking about the sheer power of them but a 7T machine doing a full scan of you, would be guaranteed nearly to find anything wrong with you.
When I last looked the full body scans for sale seemed to used 1.5T setup, which seems like a waste. The 3T advanced scans looks much more detailed, but it just depends on where you live - I couldn’t find any around.
My knee and back was years ago, so probably the 1.5T. No idea on my dogs who have had the more recent MRIs. Their scans are incredibly detailed though, so maybe the 3T?
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).
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)
> I do take slight offense to the following at the top of my results:
No offense for me, just confusion. One of the status reports started as follows:
> OptionOfT is a very pleasant 36-year-old gentleman 6 weeks status post left anterior total hip arthroplasty done by Dr. _ on _.
I asked my wife whether I was particularly friendly (I sometimes fail to adjust my demeanor in certain situations).
She said: nah, they write that for everybody.
The bar is really low for patient behavior. Tbh I find anyone not screaming at me to be pleasant in comparison.
Some RIS systems make semi form reports with ‘Dear <referrer> thank you for sending <patient> to see us for their <type of imaging> etc etc.
Then you can just tab from field to field when doing the report.
I had a nurse chart “patient ‘feels like a million bucks’” while I was getting an immunotherapy infusion.
She said “It’s just not often I hear that here.”
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 asked the oncologist if it made sense to delay the scan because of the re-excision and he said not to worry because he’d know why there’s inflammation in that area. I’m thinking the bite and the shots will probably get flagged too. I just hope I don’t forget any other maladies or mishaps that might get flagged that I can’t explain.
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?
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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.
> 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
I have multiple scans a year. "Scanxiety" is real.
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> 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.
My mum gets scanned a little more frequently than that, following treatment for an inoperable tumour in her lung around five years ago. During treatment she was getting scanned every three months or so, and it was remarkable watching this thing go from the size of a tangerine, to actually expanding a bit and looking "fuzzy" once the drugs kicked in, to being the size of a plum, then the size of a grape attached with a little thin thread of tissue, to being a thing the size of a pea. Now there's a tiny ripple of scar tissue that no-one wants to investigate further, because if it's not doing anything let's not poke at it.
There is a roughly pea-sized "thing" on her adrenal gland that was a bit worrying because anything like that is going to get intimately involved with your lymphatic system and then it's going to metastasise like hell. But it neither got bigger nor smaller in the nearly six years since the first scan, so it can't be that important.
This is one of the great things about the NHS, especially here in Scotland where we have (possibly as a result of the weirdly high levels of cancer) some of the best oncology services in the world.
If we'd lived in the US, the insurance companies would have taken one look at an 83-year-old about to become a grandmother and sent her home with a bottle of morphine to die. As it is, she's doing very well and got to see both her grandchildren start school.
> in Scotland where we have (possibly as a result of the weirdly high levels of cancer)
Interesting, I had no idea and just looked this up[0]:
> Scotland had the highest overall incidence (446 for men and 379 for women per 100 000), and Wales had the second highest rate (450 and 366 per 100 000), compared with 394 and 338 per 100 000 in England and 394 and 345 per 100 000 in Northern Ireland.
This would make Scotland rank 3rd in the table on https://en.wikipedia.org/wiki/List_of_countries_by_cancer_ra... .
PS: Glad to hear your mom is doing well!
[0]: https://pmc.ncbi.nlm.nih.gov/articles/PMC1939786/
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“MRIs…suck at cancer”
Wrong? I understand MRIs are the standard for certain types of cancer like brain and spinal tumors.
With respect to whole body MRI they can be less effective because it’s not optimized, accuracy can be traded for area.
But as a general statement MRIs do not suck at cancer.
MRIs are good if you know what you’re looking for, and usually with contrast, which in a situation like cancer where you need to do them often can result in allergic reactions.
In a full body situation, they are looking for mets, and the uptake of radioactive sugar by the tumors will let a PET scan find them.
That’s completely and 100% false. It’s much easier to characterize things on MRI and MRI is indeed phenomenal for cancer! The problem is with screening, not actual staging or follow-up, and whole-body screening in ct and pet/ct is even worse than MRI screening even if you ignore radiation.
>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.
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.
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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.
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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?
Not because of an MRI, but this happened to me:
N=1, but that biopsy should not have happened.
I don’t understand how you’re concluding that the biopsy shouldn’t have happened from that anecdote? Just because a test result is negative doesn’t mean that it shouldn’t have happened. That’s not how practicing medicine works.
Hence the N=1 I started the statement with. If we had a thousand similar situations and it turned out that in, say, 1% of cases there was a lung tumor, then we could debate whether it's worth putting 990 people through a biopsy they don't need so 10 can find out they have a tumor. Maybe that gives us the opportunity to discuss waiting a month and taking another chest x-ray (which has its own negatives) vs. doing an immediate biopsy.
But we don't have 1000 similar cases. As I said, we have 1: mine. And it turned out negative. So 1 person was put through a biopsy they didn't need, and 0 people found out they have a tumor.
Hopefully that makes my point clearer.
>MRIs are great for certain things like herniated disks in your back. They suck at cancer.
MRIs are fine for certain kinds of cancer like liver cancer.
But saying MRIs "suck at cancer" feels off. They're actually first-line or gold standard for certain cancers
I feel that label is actually deserved. Yes, some cancer types are easier to detect with MRI, in particular inside of a body, but at the same time MRI in and by itself isn't great at predicting all cancer types. How could it help with regards to leukemia, for instance? What exactly could MRI detect here better than other diagnostic tools? One has to keep in mind that diagnosis also takes time - plus the cost; and the overdiagnosis problem which means that some cancer that are not really relevant, are hyped up by MRI to be the end of the world for a patient. So there is a trade-off.
IMO MRI needs to become cheaper; and more reliable too.
hmm that is still around 1.5% of ppl having cancer. not trivial. Even more if you include false negatives.
I mean, i think you need to look more into it than that.
If you make a test that always returns true, it would also meet that criteria.
Basically half of all men have some early form of prostate cancer. Now that does not show up very well on an MRI, but there are quite a few diagnosis like that that are not necessary life saving.
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And yes getting frequent full body MRIs is still overwhelming the right thing for the patient.
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.
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
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Here in NZ an Australia, the college of radiologists disagree and say ‘don’t do it’ for screening the worried well.
https://www.ranzcr.com/college/document-library/2024-positio...
Seems like their main concern is "substantial downstream healthcare costs"
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NZ doesn't have the screening capacity for when it's medically necessary, much less optional.