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Dogs can sniff out cancer

January 2, 2017 Word for Word Media 0Comment

Currently, doctors only use three primary senses to diagnose a patient: hearing, sight, and touch. But, why use three senses when we could be using four? This is where our furry friends come in, adding the fourth sense – olfaction – to help diagnose cancer. In no way is it suggested to replace medical equipment or diagnosis; dogs are simply adding to the equation.

Searching for cancer through volatile organic compounds (VOCs) is a relatively new idea in science, with huge possibilities. Published studies from all over the world are proving accuracy levels that are beyond current available machines’ abilities. Though the negative trials, like most trials, would probably not have been published.

So why would a dog smell cancer? 

The answer is relatively simple, it’s a survival mechanism. In the ancient times, humans who were sick would have directly affected dogs. Man provided shelter and food for the dog, and in turn, the dog warned man against impeding danger, pointed towards prey and food, and, eventually, guarded our livestock and crops. We provided for the dog and the dog used his nose to help provide for, and protect, us. The key here is that the dog used his nose for our benefit. If something is wrong with us, this will affect the dog.   If we are ill, this could directly affect our ability to provide food and shelter for the dog. The dog ‘notices’ small changes which could indicate that we’re in trouble. For example, if I have a cut on my leg, under my jeans, almost every dog will find, sniff and try clean the cut. They are noticing a change, or something different from what we were before. In the dog’s mind, this small change can mean that we may become incapacitated in some way, which means the dog may suffer.

How does a dog’s nose work?

  • Dogs can smell in parts per trillion. An example of this is, a dog can smell one cc of blood, diluted into 20 Olympic-sized swimming pools.
  • It is almost impossible to understand the magnitude of a dog’s sense of smell, especially when compared to ours. We can smell chocolate cake, but a dog smells the ingredients of the cake: sugar, flour, eggs, butter, chocolate, salt, etc. This is known as layer scent, which is why they can detect your footprints on the floor, even though many other people have walked over them.
  • A dog is able to smell the hormones you emit when you’re happy, nervous, or scared. A dog doesn’t read your behaviour and body language with his eyes, he literally ‘smells’ if you’re happy or sad. He can smell the tiny amounts of perspiration or adrenaline that are emitted from your body when you’re stressed or anxious. When you cry, they try to lick it better; when you happy, they match your excitement in their behaviour.
  • Dogs can smell like we see. We walk into a room and see the room as a whole; dogs walk into the room and smell the room. Dogs smell in stereo, with each nostril splitting into two parts, one for smelling and the other for respiration. Ever heard of the saying: “Dogs are reading the newspaper when they sniff everywhere they walk”? 
  • Currently, in addition to the traditional roles such as guiding the blind and deaf, and helping the physically disabled, dogs are claimed to be able to calm autistic children, detect blood pressure changes and seizures, and, over the last decade, it has been shown they can find cancers. It’s easy to see how herding behaviour can be adapted into guide dog/medical assistance behaviour, or hunting behaviour into chemical or bio-chemical detection.


Cancer has a specific smell. One that some oncologists say is very distinctive at Stage 3 or 4, depending on the cancer. But in many of the clinical trials, dogs have been known to detect the cancer scent at Stage 0-1. The idea behind ‘cancer sniffing dogs’ is that there may be VOCs produced in cancer patients, that dogs can detect by scent, due to tumours releasing tiny amounts of alkanes and benzene derivatives not found in healthy tissue.

Training dogs to smell cancer is done in the same way that bomb and narcotic sniffing dogs are trained, pairing the target smell with a high value reward. Like teaching a puppy to sit and then rewarding her with food or her favourite toy. However, with tissue scenting, things are a little more complicated. Drugs and gun powder can be isolated, but cancer scent is one of the thousands of organic compounds within a human’s tissue. In order for the dogs to recognise the cancer scent, many samples with the common smell must be used. Also, the dogs must be trained to ignore healthy tissue scent, and all other tissue with diseases other than cancer. This means countless samples are used for training. Cancer samples, disease controls and healthy controls are needed in order for the dog to distinguish the cancer scent.

So far, several clinical trials have looked at dogs successfully recognising six cancers: lung, breast, prostate, colon, bladder and skin, by using breath, watery stools, dried urine and skin samples that seem to produce similar volatile organic molecules.

There are cancer dog training centres in Japan, EU, Hungary, US and UK; all are affiliated to medical schools and universities, and they have had a 75-98% accuracy based on trials. The samples are widespread and the dogs are trained with positive reinforcement; in the initial stages of training, they’re rewarded when they get the sample correct. They are given specific ways of reacting to the samples that are universal in that centre, such as lying down in  front of a positive sample and turning away from a control.

  • 300 samples are used to train a dog.
  • Training takes six to eight months.
  • Generalising the smell of cancer is essential.
  • Samples are not reused.
  • Trials are blind and double-blind.

MEET OUR EXPERT - Gillian Bruce

Gillian Bruce is a certified clinical case manager at ICON. Oncology is a passion of hers. She loves to learn what’s new, and working with the medical aids, doctors and patients because she believes together they make a difference.
Gillian Bruce is a certified clinical case manager at ICON. Oncology is a passion of hers. She loves to learn what’s new, and working with the medical aids, doctors and patients because she believes together they make a difference.

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