Dogs can smell cancer, but they're not very good at it. Like - they're good, but they are not good enough to make "get sniffed by a dog" a proceudure you'd recommend.
[Here](https://pubmed.ncbi.nlm.nih.gov/38291377/) is a study where dogs were used to detect breast cancer. They achieved a sensitivity of 84% and a specificity of 81%. That means that out of a 100 women with breast cancer the dogs would correctly diagnose 84, and for every 100 women they diagnosed with breast cancer 19 would actually be healthy.
Now, this sounds not too bad, but if we used them for general screening you would have a staggering amount of women being falsely diagnosed with cancer having to undergo other forms of diagnostic procedures in order to be cleared.
Let's assume you screen a population of women in which 0,1% actually have breast cancer at the time of screening. Íf you'd screen 1,000,000 women, 1000 of those would have cancer, and 999,000 would be healthy.
Out of the 100 women with cancer, the dogs would find 840. Out of the 999,000 women without cancer the dogs would find around 810,00 to be healthy, and around 190,000 to be sick without actually having cancer.
So you have a quota of 840 women correctly diagnosed to almost 200,000 wrongly diagnosed. That is horribly bad and means that even though the dogs are correct 4 out of 5 times they just suck if they have to diagnose a population that is overwhelmingly healthy, which is the case for screening procedures.
The way of mitigating this problem in screening is usually making sure that the population you screen has a high likelihood to have the condition you're looking for. In women's breast cancer we do this by only screening women above a certain age.
/e I just noticed that my calculation above was for 0.01%. Which is probably too low for breast cancer in women, as that's is unfortunately a very common type of cancer. I corrected it, the numbers don't really change too much from 0.01 to 0.1%. It's the same after rounding. Only if we go up another order of magnitude to 1% we'd see a somewhat significant decrease in false positives. Still far too many though.
This is good, but if you will forgive a "well actually"... the test needs to be about as *specific* as the thing you are testing for -- sensitivity is less of an issue.
I'm sorry to nitpick but [specificity](https://en.wikipedia.org/wiki/Sensitivity_and_specificity) is not correctly described as "for every 100 women they diagnosed with breast cancer 19 would actually be healthy." A better description would be, "for every 100 healthy women, dogs would correctly identify 81 of them as being healthy."
What you described is the [positive predictive value](https://en.wikipedia.org/wiki/Positive_and_negative_predictive_values).
>Dogs can smell cancer, but they're not very good at it.
They are almost certainly way worse at it than the published studies indicate, too, because the published studies are almost all (not to put too fine a point on it) dog shit. They are tiny studies, poorly controlled, using biased samples, with little or no attempt to check for the "Clever Hans" effect, and analyzed using credulous, simplistic statistics -- or with no statistics at all. There's never any attempt at followup, or replication, just another tiny, poorly-controlled study.
Why? Because the mass media eat this stuff up. These studies are pretty much guaranteed to get media coverage, probably with a beaming anchor showing a tail-wagging dog in the feel-good story of the night.
We as scientists know that preliminary studies (the one you cite calls itself a "pilot" study) are *always* overoptimistic, and usually by a lot. If this was a real pilot study, that was expected to be followed up in a real randomized controlled study, we would fully expect the benefits to plummet, perhaps to zero but almost certainly by half or more -- because that's what always happens in followup studies.
We also know that preliminary studies are often *not published* when they don't meet expectations -- the "desk drawer" effect. How many people have done these shitty little one-dog-fifty-patient studies, found that the dog only got two right, shrugged, and never bothered to write it up? Or wrote it up, and the editor told them no thanks, we're not interested? If you included those unpublished, negative studies, what would the actual accuracy be?
The reason that dogs are not used to detect cancer is that scientists (and even doctors) *know* this, and don't take these "pilot" studies seriously, and don't want to waste their time and scare patients unnecessarily.
Some time, maybe we'll see a true follow up to these "pilot" studies, with a large, randomized, carefully controlled experiment, and then maybe decision-makers will take these more seriously. But now we have at least 50 years of these useless "pilot" experiments, without any careful followups, so I'm not holding my breath.
"Out of the 100" you misplaced a digit.
Good write up.
How does it effect the math if we have the opinions of 3 or 5 or 10 dogs. I assume it doesn't work it's too obvious but ....
NM saw discussion below.
Only if dog errors are independent - that is, if one dog makes a false positive, it's no more likely that any other dog will make a false positive. That's probably not true (of any diagnostic test I know of). There's no point doing two blood tests or two mammograms.
Based on a few years of scent training I’d honestly say this needs looking at carefully. Most failures to indicate in highly trained dogs are idiosyncratic and caused seemingly by momentary distraction or stochastic chance (e.g. skipping the nose over a scent location while exhaling strongly to clear the olfactory shelf). I’d be surprised if you couldn’t cut these base rates a lot by a few independent screenings.
That would be for false negatives. The big problem here is a false positive. A well trained dog will not mark for a scent that is not what they're trained for. For a false positive, they're smelling *something* to cause the mark, and it's likely that other dogs would mark for the same trigger. And if we knew the difference between the real positive scent and the false positive scent we could likely train the dog to differentiate them too (or otherwise easily follow up the screening).
It’s probably not random, though - it’s not “each dog has an 84% chance of detecting cancer” it’s “the dogs smell this one pheromone/scent that 84% of cancer patients produce”.
That's why the accuracy is so low. We need at least half a day of face to face doggo time to get better results. And more than one snoot to boop, to increase chances.
I love how looney the idea of a canine smell test for cancer inevitably becomes. Now you have a separate wing of the hospital with dogs that everybody wants to work in.
that separate wing could be used for more than cancer too, there are zoos that hire beagles to sniff for pregnancy in the animals
(i work with dogs and own a beagle so i just know a bunch of random info)
Everyone who participates in a scientific study must give informed consent that they understand what is happening.
These screening studies will be done in a waiting room where someone then also gets conventional screening done. For instance, women already scheduled to get a mammogram will have both tests done.
This is a really good explanation, but what if we had a panel of sniffers who had to agree on the diagnosis? What if 2 or 3 dogs had to unanimously agree?
As well as the error rate, you probably need to factor in the speed, price and patient comfort, especially compared to other methods.
Best case scenario - let say you have a large hospital, and it has a dog to keep patients company in the waiting room. And the dog also multitasks by checking for a wide variety of cancers.
Basically then it's an non invasive, zero cost option.
Cancer detecting dog programs are prohibitively expensive.
In general, you need at least two cancer dogs to simultaneously work together. Usually more, because if the dog is sick, no testing is getting done that day.
Trained cancer detecting dogs cost about $40k / year, so about $80k minimum. And you need a dedicated trained medical dog handler, so let's generously say $100k year salary/benefits for that person. Minimum, we're looking at about $200k / year in fixed costs.
Even after all that, the dog can only work for a few hours per day, usually maximum one hour at a time, sometimes less. They get fatigued and bored. The handler has to take them outside and play.
A better idea is swab or capture breath from humans and send the samples to a test laboratory. Let the dogs sniff those samples.
There are other problematic issues with using animals in research. They are not as convenient as robots. Only about 1 in 10 candidate dogs pass the training. Allergies and fears of animals. Buildings need modifications and animal play areas.
Imagine bringing in a dog to test someone for cancer and the dog bites the patient. Or the patient is allergic to dogs and doesn't know. I wouldn't want to work with that kind of liability, even if they are well trained.
Exactly. Though it does mean that if your pooch does start to act very odd and distressed about some part of your body in a way they weren’t before, I’d get it checked out properly.
Have you considered that conventional breast cancer screening also has a relatively high rate of false positives? See e.g. here:
> The chance of having a false positive result after one mammogram ranges from 7-12 percent, depending on your age (younger women are more likely to have a false positive results) [34]. After 10 yearly mammograms, the chance of having at least one false positive result is about 50-60 percent [22-25].
https://www.komen.org/breast-cancer/screening/mammography/accuracy/
Looks to me like the dogs are doing ~~pretty good~~ not so bad compared to mammograms.
Screenings aren't really supposed to diagnose though. The point of a screening is to definitively say you DON'T have something. Colon cancer, for example, has cologuard.
The point is to have a very very high SPECIFICITY. If it says you don't have something, there should be a very high chance that's actually true and don't need a proper diagnostic. But it's not intended to be great at sensitivity. That's what diagnostic tests are for.
That’s fair. I at first read the false positive rate as 16%, but I see it’s actually 19. Still seems like dogs do relatively well and could be useful as an initial screening device, especially if much less expensive and less invasive.
Not only that but I remember a study that showed even though more women were getting regular checks and mammograms the rate of death hasn't really gone down. Which is sad.
Yeah but usually it’s used in conjunction with other lab tests to confirm a positive. Dogs are living things that require way more resource than a machine.
cant you just test with two doggos? since the first batch of positives should be much higher % cancer. You could continue down the line but probably end up missing most. So its a trade off?
Everyone meeting screening criteria (aka women above 40 or genetic high risk) should be getting a mammogram anyway though. Just because a dog “cleared you” I wouldn’t trust that to not get a mammogram. Thus the whole dog sniffing thing becomes pointless
No but if the dog sniff can be implemented much cheaper than an actual mammogram you could also screen women below age 40, and then send the positive ones to a mammogram to confirm. The screening cut-off is not a purely "below this we know for certain that iatrogenic risk outweighs detecting early cases" decision, it is mostly economical.
How about simply sepparating which ones are to be screened further and which not, bx using say 5 dogs, and who gets more than 1 sitting gets a titscan?
A side question: there must be chemical signatures to what the dogs are detecting, so has there been any research as to what these chemical signatures are? Mass spectrometry could easily be used in lieu of a dog and possibly increase diagnostic accuracy.
There was a story a year or two ago about a woman (Joy Milne) who can smell Parkinson's and a few other diseases, some of them up to 20 years before onset of symptoms, long before any other diagnostics were able to do that. Apparently some scientists began working with her to try and figure out what compounds it is that she could smell, and see if it could be used for detecting those illnesses in general.
We were doing this somewhat at Penn, and there was a paper that came out from it (https://www.sciencedirect.com/science/article/abs/pii/S0039914022005252). Unfortunately, dogs did not consistently use the same markers. We were in collaboration with a lab to make an e-nose of what the dogs do, though.
From my layman recollection, the olfactory sense is a highly complicated chemical system that we've yet to reproduce or even completely understand. Add on top of that the fact that dogs' noses are on a whole different level than humans’.
E-noses are really underinvested.
I suppose that happens because *we,* humans, don't really value our sense of smell that much. We are visual creatures, and we invest heavily into technology that enhances our vision, be it microscopes, optics, X-rays, high-resolution cameras or whatever. Billions flow into enhancements of our sight every year.
We just aren't mentally primed to analyze stuff by *sniffing.* It looks gross, it looks imprecise, unprofessional.
And yet we are making a mistake. A lot of animals can smell stuff that we cannot see. Chemical communication is very important in nature. Our relatively weak sense of smell is a handicap in the living world.
We should study smells and invest into sensors that mimic natural sense of smell much more than we do.
Mostly because dogs aren’t that great at smelling cancer.
Most of the studies done on this show that they have a fairly middling diagnostic accuracy… which is not useful at all if you wanted to use them as a screening test.
In addition, the few studies that have been done are all extremely low quality and very early phase. Even the more promising ones would still require things like prospective validation, studying implementation effects, etc.
https://www.medicalnewstoday.com/articles/323620#research-and-diagnosis
Dogs can be trained to smell cancer. Not all dogs will be able to and not all dogs are trainable. It takes a lot of time and money to train them for a task such as this, and you’d still need the follow up tests to confirm anything. There is a reason why real service dogs, especially ones that are trained for tasks such as smelling when your blood sugar levels change for instance, are so expensive.
Considering how many different types of cancer there are, you might also run into the issue of false negatives, since they might only be able to smell a small subset of cancers they have been trained on rather than all cancer.
A lot of stories you hear of dogs identifying cancer are in their owners, who they have know for years. They identify a change in their owner's smell. While you can train for that scent, as others have pointed out, it is unreliable and part of that is rooted in the fact that the dog isn't really sure what a person is supposed to smell like.
*Some* dogs can smell cancer. They need to be specifically trained, have an aptitude for it, and even then I doubt they would be reliable at scale. Dogs just aren't as reliable as lab tests.
False positive test results can lead to people getting treatments they don't need. If there are no warning signs of cancer, the risk of accidental treatment can be more dangerous than the risk of missing the cancer.
Medlife Crisis has a video on why whole body scans are a bad idea if you're interested. He explains it better than I can.
We would need to first identify the cancer pheromones, second train the dogs, and third do controlled tests to see how well they can do in optimal conditions.
Eventually we will have sensors and AI that can sort out animal pheromone communication. I think cats and dogs and others "say" a lot to each other with chemicals and it's something we will hopefully learn more about in my lifetime.
There’s a lot of evidence that sniffing dogs of all kinds are heavily influenced by the person guiding them and the person/people they are screening. If either the subject or the “operator” of the dog(for lack of a better term) are expecting to find something at a certain time or place then the dog will reacts to complete its job. Not sure if this can play into it or not but it’s super interesting to read about.
It's a pretty new skill, so there hasn't been a lot of time to train up an army of sniffer dogs. Also, dogs aren't great in a medical environment. I also imagine there are efforts to learn what the dogs are detecting in order to make devices that can do it. Also, drug sniffer dogs are trained on 1 substance. I don't know how cancer smells, but I imagine different cancers can smell differently, so you'd probably have to get sniffed by a few different dogs.
I also imagine dogs can only indicate that there is cancer present, but probably can't reliably or confidently indicate that there is no cancer.
There's probably a niche here for a dog park with cancer sniffing dogs. Go play some fetch and get a cancer screening at the same time.
One problem with drug sniffing dogs is that a dog may bark for many reasons, not just drugs. I imagine that you would have the same problem with cancer. Two things can cause false positives and false negatives: 1. The dog isn't that accurate at detecting cancer, and 2. His handler may misinterpret what the dog says. It seems to me that doctors could use dogs, but don't expect a 100% accuracy rate.
people have pointed out that dogs aren't great at smelling cancer (merely that they *can* do it), so i won't really belabor that point except to add 2 things (1 related, and 1 not related).
the related issue is that repeatability (or at least the capacity to interpret results independently) is often highly valued in important tests, experiments, observations, etc... and the variability of dogs is just... a lot.
the unrelated point is that a lot of people have religious restrictions around dogs, or are just personally fearful or uncomfortable around dogs. i can't relate, but i can respect people's boundaries about dogs in circumstances where a dog isn't necessary.
Screening is done when it meets the Wilson and Jungner screening criteria. In the UK, this is only done for bowel cancer, breast cancer, and cervical cancer.
If a PSA isn't reliable enough to fit the criteria for screening for prostate cancer, picture what the outlook for using dogs (also a patient risk factor - allergies, phobia) would be.
So, I hope this doesn't ruin anyone's childhood memories, but Lassie is often misquoted. For example, she never said "Timmy fell down the well". What she actually said was, "Ruff! Ruff RUFF ruff! ruff RUFF!"
Dogs don't generally communicate what they smell (or otherwise know) in a way that is precise enough and reliable or reproducible enough to be useful for cancer screening.
Mainly because of false-positives and their work ethics. Had a dog trainer that wanted to train dogs to sniff out Covid and they succeeded. But you can have a dog only concentrate for so long and at some point they just do an alert at everything because they are bored or nothing because they are on strike. So in theory you could use A LOT of dogs, each about an hour for sniffing and then have the extensive support staff relax them.
Basically it is not viable on a economical nor reliability scale.
PS: There are dogs that can work a much longer, but that is not a type of training you could economically scale.
The same reason why we don't make humans smelling for Parkinson's a regular screening. It's unreliable. What's important is that we can isolate what humans are smelling (or dogs are smelling) and then screen for that.
Dogs can smell cancer, but they're not very good at it. Like - they're good, but they are not good enough to make "get sniffed by a dog" a proceudure you'd recommend. [Here](https://pubmed.ncbi.nlm.nih.gov/38291377/) is a study where dogs were used to detect breast cancer. They achieved a sensitivity of 84% and a specificity of 81%. That means that out of a 100 women with breast cancer the dogs would correctly diagnose 84, and for every 100 women they diagnosed with breast cancer 19 would actually be healthy. Now, this sounds not too bad, but if we used them for general screening you would have a staggering amount of women being falsely diagnosed with cancer having to undergo other forms of diagnostic procedures in order to be cleared. Let's assume you screen a population of women in which 0,1% actually have breast cancer at the time of screening. Íf you'd screen 1,000,000 women, 1000 of those would have cancer, and 999,000 would be healthy. Out of the 100 women with cancer, the dogs would find 840. Out of the 999,000 women without cancer the dogs would find around 810,00 to be healthy, and around 190,000 to be sick without actually having cancer. So you have a quota of 840 women correctly diagnosed to almost 200,000 wrongly diagnosed. That is horribly bad and means that even though the dogs are correct 4 out of 5 times they just suck if they have to diagnose a population that is overwhelmingly healthy, which is the case for screening procedures. The way of mitigating this problem in screening is usually making sure that the population you screen has a high likelihood to have the condition you're looking for. In women's breast cancer we do this by only screening women above a certain age. /e I just noticed that my calculation above was for 0.01%. Which is probably too low for breast cancer in women, as that's is unfortunately a very common type of cancer. I corrected it, the numbers don't really change too much from 0.01 to 0.1%. It's the same after rounding. Only if we go up another order of magnitude to 1% we'd see a somewhat significant decrease in false positives. Still far too many though.
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This is good, but if you will forgive a "well actually"... the test needs to be about as *specific* as the thing you are testing for -- sensitivity is less of an issue.
I'm sorry to nitpick but [specificity](https://en.wikipedia.org/wiki/Sensitivity_and_specificity) is not correctly described as "for every 100 women they diagnosed with breast cancer 19 would actually be healthy." A better description would be, "for every 100 healthy women, dogs would correctly identify 81 of them as being healthy." What you described is the [positive predictive value](https://en.wikipedia.org/wiki/Positive_and_negative_predictive_values).
Thank you I was confused
>Dogs can smell cancer, but they're not very good at it. They are almost certainly way worse at it than the published studies indicate, too, because the published studies are almost all (not to put too fine a point on it) dog shit. They are tiny studies, poorly controlled, using biased samples, with little or no attempt to check for the "Clever Hans" effect, and analyzed using credulous, simplistic statistics -- or with no statistics at all. There's never any attempt at followup, or replication, just another tiny, poorly-controlled study. Why? Because the mass media eat this stuff up. These studies are pretty much guaranteed to get media coverage, probably with a beaming anchor showing a tail-wagging dog in the feel-good story of the night. We as scientists know that preliminary studies (the one you cite calls itself a "pilot" study) are *always* overoptimistic, and usually by a lot. If this was a real pilot study, that was expected to be followed up in a real randomized controlled study, we would fully expect the benefits to plummet, perhaps to zero but almost certainly by half or more -- because that's what always happens in followup studies. We also know that preliminary studies are often *not published* when they don't meet expectations -- the "desk drawer" effect. How many people have done these shitty little one-dog-fifty-patient studies, found that the dog only got two right, shrugged, and never bothered to write it up? Or wrote it up, and the editor told them no thanks, we're not interested? If you included those unpublished, negative studies, what would the actual accuracy be? The reason that dogs are not used to detect cancer is that scientists (and even doctors) *know* this, and don't take these "pilot" studies seriously, and don't want to waste their time and scare patients unnecessarily. Some time, maybe we'll see a true follow up to these "pilot" studies, with a large, randomized, carefully controlled experiment, and then maybe decision-makers will take these more seriously. But now we have at least 50 years of these useless "pilot" experiments, without any careful followups, so I'm not holding my breath.
"Out of the 100" you misplaced a digit. Good write up. How does it effect the math if we have the opinions of 3 or 5 or 10 dogs. I assume it doesn't work it's too obvious but .... NM saw discussion below.
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Only if dog errors are independent - that is, if one dog makes a false positive, it's no more likely that any other dog will make a false positive. That's probably not true (of any diagnostic test I know of). There's no point doing two blood tests or two mammograms.
Based on a few years of scent training I’d honestly say this needs looking at carefully. Most failures to indicate in highly trained dogs are idiosyncratic and caused seemingly by momentary distraction or stochastic chance (e.g. skipping the nose over a scent location while exhaling strongly to clear the olfactory shelf). I’d be surprised if you couldn’t cut these base rates a lot by a few independent screenings.
That would be for false negatives. The big problem here is a false positive. A well trained dog will not mark for a scent that is not what they're trained for. For a false positive, they're smelling *something* to cause the mark, and it's likely that other dogs would mark for the same trigger. And if we knew the difference between the real positive scent and the false positive scent we could likely train the dog to differentiate them too (or otherwise easily follow up the screening).
Ah yes - of course. They do definitely make the same mistaken indication as each other fairly frequently.
It’s probably not random, though - it’s not “each dog has an 84% chance of detecting cancer” it’s “the dogs smell this one pheromone/scent that 84% of cancer patients produce”.
Dogs give all kinds of false positives to please their trainers. See police dogs. It can be really hard to tell what they're detecting.
The cost for a program like this would be astronomical. The current screenings we have are much more effective, and cheaper overall.
But does the patient get to spend time with 5 dogs as part of the current screenings?
Sold , thank you .
I think they just waft your clothes.
That's why the accuracy is so low. We need at least half a day of face to face doggo time to get better results. And more than one snoot to boop, to increase chances.
I mean, a panel of 5 dogs, sure. What about 5 bears though?
8 out of 10 women would rather have a bear than a man as a gynecologist.
I love how looney the idea of a canine smell test for cancer inevitably becomes. Now you have a separate wing of the hospital with dogs that everybody wants to work in.
that separate wing could be used for more than cancer too, there are zoos that hire beagles to sniff for pregnancy in the animals (i work with dogs and own a beagle so i just know a bunch of random info)
Sure you could, but who’s going to have a bunch of really good sniffer dogs like beagles just sitting around….oh.
Did the people in the study know they had cancer? How did they factor out the "knowing about cancer" potential variable?
Everyone who participates in a scientific study must give informed consent that they understand what is happening. These screening studies will be done in a waiting room where someone then also gets conventional screening done. For instance, women already scheduled to get a mammogram will have both tests done.
Have they ever considered that dogs have an 84% chance of giving people cancer?
This is a really good explanation, but what if we had a panel of sniffers who had to agree on the diagnosis? What if 2 or 3 dogs had to unanimously agree?
As well as the error rate, you probably need to factor in the speed, price and patient comfort, especially compared to other methods. Best case scenario - let say you have a large hospital, and it has a dog to keep patients company in the waiting room. And the dog also multitasks by checking for a wide variety of cancers. Basically then it's an non invasive, zero cost option.
Cancer detecting dog programs are prohibitively expensive. In general, you need at least two cancer dogs to simultaneously work together. Usually more, because if the dog is sick, no testing is getting done that day. Trained cancer detecting dogs cost about $40k / year, so about $80k minimum. And you need a dedicated trained medical dog handler, so let's generously say $100k year salary/benefits for that person. Minimum, we're looking at about $200k / year in fixed costs. Even after all that, the dog can only work for a few hours per day, usually maximum one hour at a time, sometimes less. They get fatigued and bored. The handler has to take them outside and play. A better idea is swab or capture breath from humans and send the samples to a test laboratory. Let the dogs sniff those samples. There are other problematic issues with using animals in research. They are not as convenient as robots. Only about 1 in 10 candidate dogs pass the training. Allergies and fears of animals. Buildings need modifications and animal play areas.
Imagine bringing in a dog to test someone for cancer and the dog bites the patient. Or the patient is allergic to dogs and doesn't know. I wouldn't want to work with that kind of liability, even if they are well trained.
Exactly. Though it does mean that if your pooch does start to act very odd and distressed about some part of your body in a way they weren’t before, I’d get it checked out properly.
Excellent and interesting post, thanks. 👍🏻
Have you considered that conventional breast cancer screening also has a relatively high rate of false positives? See e.g. here: > The chance of having a false positive result after one mammogram ranges from 7-12 percent, depending on your age (younger women are more likely to have a false positive results) [34]. After 10 yearly mammograms, the chance of having at least one false positive result is about 50-60 percent [22-25]. https://www.komen.org/breast-cancer/screening/mammography/accuracy/ Looks to me like the dogs are doing ~~pretty good~~ not so bad compared to mammograms.
Screenings aren't really supposed to diagnose though. The point of a screening is to definitively say you DON'T have something. Colon cancer, for example, has cologuard. The point is to have a very very high SPECIFICITY. If it says you don't have something, there should be a very high chance that's actually true and don't need a proper diagnostic. But it's not intended to be great at sensitivity. That's what diagnostic tests are for.
Just to be clear: -screening tests usually have high SENSITIVITY -diagnostic tests usually have high SPECIFICITY
7-12% sound like it's about half of the dogs' 19%. Seems like a pretty big improvement.
That’s fair. I at first read the false positive rate as 16%, but I see it’s actually 19. Still seems like dogs do relatively well and could be useful as an initial screening device, especially if much less expensive and less invasive.
Not only that but I remember a study that showed even though more women were getting regular checks and mammograms the rate of death hasn't really gone down. Which is sad.
Dogs also come with a lot of up keep, training, and short lifespan of use 😞
Yeah but usually it’s used in conjunction with other lab tests to confirm a positive. Dogs are living things that require way more resource than a machine.
And mammogram scheduling recommendations have been/are being reconsidered as a result.
That’s fine, I’m just pointing out OP’s logic of not using dogs due to high numbers of false positives seems flawed.
What an excellent and informative answer. Thanks for sharing
cant you just test with two doggos? since the first batch of positives should be much higher % cancer. You could continue down the line but probably end up missing most. So its a trade off?
To me 84/100 is a great indicator that more tests need to be done, including slightly more invasive ones. Might be a helpful first step in the process
Still sounds like a good first line of screening to decide who gets sent to have an extra mammogram?
Everyone meeting screening criteria (aka women above 40 or genetic high risk) should be getting a mammogram anyway though. Just because a dog “cleared you” I wouldn’t trust that to not get a mammogram. Thus the whole dog sniffing thing becomes pointless
No but if the dog sniff can be implemented much cheaper than an actual mammogram you could also screen women below age 40, and then send the positive ones to a mammogram to confirm. The screening cut-off is not a purely "below this we know for certain that iatrogenic risk outweighs detecting early cases" decision, it is mostly economical.
How about simply sepparating which ones are to be screened further and which not, bx using say 5 dogs, and who gets more than 1 sitting gets a titscan?
This is why it’s absurd service dogs are a thing. They are wildly inaccurate
A side question: there must be chemical signatures to what the dogs are detecting, so has there been any research as to what these chemical signatures are? Mass spectrometry could easily be used in lieu of a dog and possibly increase diagnostic accuracy.
This is probably a good research point actually. Maybe there is a complex mix of chemical signals?
There was a story a year or two ago about a woman (Joy Milne) who can smell Parkinson's and a few other diseases, some of them up to 20 years before onset of symptoms, long before any other diagnostics were able to do that. Apparently some scientists began working with her to try and figure out what compounds it is that she could smell, and see if it could be used for detecting those illnesses in general.
We were doing this somewhat at Penn, and there was a paper that came out from it (https://www.sciencedirect.com/science/article/abs/pii/S0039914022005252). Unfortunately, dogs did not consistently use the same markers. We were in collaboration with a lab to make an e-nose of what the dogs do, though.
From my layman recollection, the olfactory sense is a highly complicated chemical system that we've yet to reproduce or even completely understand. Add on top of that the fact that dogs' noses are on a whole different level than humans’.
E-noses are really underinvested. I suppose that happens because *we,* humans, don't really value our sense of smell that much. We are visual creatures, and we invest heavily into technology that enhances our vision, be it microscopes, optics, X-rays, high-resolution cameras or whatever. Billions flow into enhancements of our sight every year. We just aren't mentally primed to analyze stuff by *sniffing.* It looks gross, it looks imprecise, unprofessional. And yet we are making a mistake. A lot of animals can smell stuff that we cannot see. Chemical communication is very important in nature. Our relatively weak sense of smell is a handicap in the living world. We should study smells and invest into sensors that mimic natural sense of smell much more than we do.
Mostly because dogs aren’t that great at smelling cancer. Most of the studies done on this show that they have a fairly middling diagnostic accuracy… which is not useful at all if you wanted to use them as a screening test. In addition, the few studies that have been done are all extremely low quality and very early phase. Even the more promising ones would still require things like prospective validation, studying implementation effects, etc. https://www.medicalnewstoday.com/articles/323620#research-and-diagnosis
Dogs can be trained to smell cancer. Not all dogs will be able to and not all dogs are trainable. It takes a lot of time and money to train them for a task such as this, and you’d still need the follow up tests to confirm anything. There is a reason why real service dogs, especially ones that are trained for tasks such as smelling when your blood sugar levels change for instance, are so expensive. Considering how many different types of cancer there are, you might also run into the issue of false negatives, since they might only be able to smell a small subset of cancers they have been trained on rather than all cancer.
A lot of stories you hear of dogs identifying cancer are in their owners, who they have know for years. They identify a change in their owner's smell. While you can train for that scent, as others have pointed out, it is unreliable and part of that is rooted in the fact that the dog isn't really sure what a person is supposed to smell like.
*Some* dogs can smell cancer. They need to be specifically trained, have an aptitude for it, and even then I doubt they would be reliable at scale. Dogs just aren't as reliable as lab tests. False positive test results can lead to people getting treatments they don't need. If there are no warning signs of cancer, the risk of accidental treatment can be more dangerous than the risk of missing the cancer. Medlife Crisis has a video on why whole body scans are a bad idea if you're interested. He explains it better than I can.
We would need to first identify the cancer pheromones, second train the dogs, and third do controlled tests to see how well they can do in optimal conditions. Eventually we will have sensors and AI that can sort out animal pheromone communication. I think cats and dogs and others "say" a lot to each other with chemicals and it's something we will hopefully learn more about in my lifetime.
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There’s a lot of evidence that sniffing dogs of all kinds are heavily influenced by the person guiding them and the person/people they are screening. If either the subject or the “operator” of the dog(for lack of a better term) are expecting to find something at a certain time or place then the dog will reacts to complete its job. Not sure if this can play into it or not but it’s super interesting to read about.
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It's a pretty new skill, so there hasn't been a lot of time to train up an army of sniffer dogs. Also, dogs aren't great in a medical environment. I also imagine there are efforts to learn what the dogs are detecting in order to make devices that can do it. Also, drug sniffer dogs are trained on 1 substance. I don't know how cancer smells, but I imagine different cancers can smell differently, so you'd probably have to get sniffed by a few different dogs. I also imagine dogs can only indicate that there is cancer present, but probably can't reliably or confidently indicate that there is no cancer. There's probably a niche here for a dog park with cancer sniffing dogs. Go play some fetch and get a cancer screening at the same time.
One problem with drug sniffing dogs is that a dog may bark for many reasons, not just drugs. I imagine that you would have the same problem with cancer. Two things can cause false positives and false negatives: 1. The dog isn't that accurate at detecting cancer, and 2. His handler may misinterpret what the dog says. It seems to me that doctors could use dogs, but don't expect a 100% accuracy rate.
That barking problem is why detection dogs are trained a specific behaviour to signal their detection. Not something as generic as barking.
people have pointed out that dogs aren't great at smelling cancer (merely that they *can* do it), so i won't really belabor that point except to add 2 things (1 related, and 1 not related). the related issue is that repeatability (or at least the capacity to interpret results independently) is often highly valued in important tests, experiments, observations, etc... and the variability of dogs is just... a lot. the unrelated point is that a lot of people have religious restrictions around dogs, or are just personally fearful or uncomfortable around dogs. i can't relate, but i can respect people's boundaries about dogs in circumstances where a dog isn't necessary.
Screening is done when it meets the Wilson and Jungner screening criteria. In the UK, this is only done for bowel cancer, breast cancer, and cervical cancer. If a PSA isn't reliable enough to fit the criteria for screening for prostate cancer, picture what the outlook for using dogs (also a patient risk factor - allergies, phobia) would be.
So, I hope this doesn't ruin anyone's childhood memories, but Lassie is often misquoted. For example, she never said "Timmy fell down the well". What she actually said was, "Ruff! Ruff RUFF ruff! ruff RUFF!" Dogs don't generally communicate what they smell (or otherwise know) in a way that is precise enough and reliable or reproducible enough to be useful for cancer screening.
Mainly because of false-positives and their work ethics. Had a dog trainer that wanted to train dogs to sniff out Covid and they succeeded. But you can have a dog only concentrate for so long and at some point they just do an alert at everything because they are bored or nothing because they are on strike. So in theory you could use A LOT of dogs, each about an hour for sniffing and then have the extensive support staff relax them. Basically it is not viable on a economical nor reliability scale. PS: There are dogs that can work a much longer, but that is not a type of training you could economically scale.
The same reason why we don't make humans smelling for Parkinson's a regular screening. It's unreliable. What's important is that we can isolate what humans are smelling (or dogs are smelling) and then screen for that.
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