Science Questions

Can dogs really smell cancer?

Tue, 10th Nov 2015

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Destiny asked:

How do dogs sniff out cancer?


Dogs have an extremely strong sense of smell but do they have a role to play in advancing medical science? Kat Arney and Chris Smith sniffed out the answer to Destiny's question...

Jobi detection dogKat - This is one of my favourite things because I've actually been to visit the medical detection dogs. They have a little centre outside Milton Keynes. And yes, there are chemicals. They call them volatile molecules that are given off by cancers and dogs can detect them. And there's various anecdotal stories about owners who noticed their dog kind of pawing at them or worrying at them, and then they were diagnosed with cancer. There are also some experiments, lab tests, if you will, that have been done showing that dogs can pick up some of the smells given off by tumours – various different types of cancers. If they're highly trained – we’re talking about highly trained sniffer dogs here – they can be trained to reliably sniff out cancers. There's currently a clinical trial going on in the UK looking at big things like prostate and bladder cancer by getting dogs to sniff people's wee. The thing about the dogs though is that it's all very interesting, but you can't imagine a dog in every surgery up and down the country because these are very highly trained dogs. They're highly trained to certain types of cancers because different cancers will give off different molecules. So, the universal lab test (I just like saying that, better than a CAT scan) is not going to be really practical. But what could be really useful is if we can work out, what are the molecules that these dogs are smelling? because at the moment, it’s really hard to tell the difference between aggressive tumours and tumours that aren’t growing very fast. If we could work out, what are the dogs smelling? and then develop an electronic sensor, kind of an e-nose that could sniff out those molecules then that is the basis of a much more widely applicable test. So, I think the dog stuff, it's really interesting and they're very, very cute and they work really well. But I think certainly, if we can find out what they're telling us, that could be extremely useful.

Chris - This is sort of the field of metabolomics, isn't it? scientists are now beginning to detect various diseases by not looking for individual genes or individual markers in and of themselves related to a disease. They're saying, "Let’s measure lots of chemicals all at once in lots of people who have a condition" and what we’ll see is that in people who have that condition, there may be some of those chemicals that are changed just very subtly and individually, very small change, but taken as a population of changes, you’ve actually got a very sensitive test. When I was in Geneva a couple of weeks ago at a conference run by the drug company Merck where they were bringing research scientists together from across Africa, I met a chap from South Africa who had invented a breath test for TB and a blood test. The way this works is that when you have TB and you come in to the laboratory, and you give samples to try and tell if you’ve got tuberculosis, it can take a month before you get the diagnosis which if you've already had to trek along way from a remote area, a doctor to get the diagnosis, that's a problem. His technique means you take a blood sample, you look at lots of different markers in the blood, and he can tell with more than 99.9 per cent sensitivity whether or not a person has got tuberculosis just from a blood sample and he can do it in 15 minutes.

Kat - Yeah. The idea of breath tests and blood tests for cancers are certainly very exciting. I think it's definitely one to watch over the next couple of years.


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A dog's sense of smell is a highly tuned analytical tool. Dogs are able to infer from low level data, especially if they are treated and trained so they have incentive to analyze certain data. For example, a good tracking dog can smell and detect single skin cells. Our skin constantly defoliates dead skin cells, as a person walks and moves. These are on our clothes and we leave a trail of skin cells with our unique scene as we walk. Skill track dogs can follow this trail.

Cancer cells have their own scent. These do not fall off like skin cells, but a collection of these, can result in certain odors being present on the body that a dog can be trained to notice. Skin cancer would be easy for a dog to detect, since these are on the surface. The body fights cancer with the waste ending up in the digestive track for recycle. This makes your solid and liquid waste, have a certain smell dogs could be trained to detect. Dogs like sniffing butts anyway, to determine eating history and other parameters. We could train the dog to notice other parameters such as scent marker drugs that trigger if cancer is present.
puppypower, Sat, 10th Oct 2015

I think that given this report "The woman who can smell Parkinson's disease"
I would think it highly likely dogs could be trained to detect certain illnesses. Colin2B, Fri, 23rd Oct 2015

"Dogs can help doctors “smell” cancer? It may sound incredible, but in fact, this research has made great progress. Recently, the “Cancer Sniffing Dogs Project”, approved by the British NHS, has entered the testing phase. Milton Keynes University Hospital of Buckinghamshire also approved this research program proposed by a charity organization. This is what I read in the article Can Dogs Smell Cancer by Creative Biolabs.

Candy Swift, Mon, 26th Oct 2015

A wife of a man with Parkinsons disease noticed that his odor changed when he came down with it. Scientists tested her ability and conformed the skill she picked up. In a blind quiz she picked out 11 of the 12 people who had parkinsons disease by smelling shirts they had previously worn . Even more, the 12th person she guessed wrongly on was diagnosed a few months later. jazzderry, Tue, 27th Oct 2015

Scientists at Cambridge University have been developing a breath test for Parkinson's, which works in basically the same way chris, Tue, 27th Oct 2015

So is the lady smelling a kind of waste product? Is sweat a way for the body to get rid of toxins and wastes from the whole body including the brain?

On a couple of occasions when I've been in the company of an old person who didn't have long left to live I thought I could smell a distinctive odor! I don't mean the 'old person smell.' It's very distinctive and even now I can smell the odor in my head! Am I actually smelling the breakdown of bodily tissue? or what? Is this possible? Harri, Tue, 27th Oct 2015

This article about the Milton Keynes trial on prostrate cancer suggests that cancer cells could produce volatile (smelly) compounds in urine
The current test for prostrate cancer PSA looks for a protein which may well have a smell passed to urine.
Diabetics can produce ketones which makes the breath smell of rotten apples.
I suspect there are many processes in the body during illness that will produce a scent a dog would detect as being unusual. Whether the scent is in sweat, breath, urine would depend on the chemicals and how they are released. Colin2B, Wed, 28th Oct 2015

A possible explanation how Parkinson's can change body odour ? ...

Parkinson's disease reduces dopamine levels.
Reduced dopamine levels can cause hyperprolactinaemia.
Hyperprolactinaemia reduces the level of sex-hormones.
Reduction in level of sex-hormones changes the person's body-odour. RD, Wed, 28th Oct 2015

A dog can detect scent traces of 2 parts per million in normally circulating air, so it's highly likely imo. ritchie, Wed, 28th Oct 2015

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