Can a Dog Smell Cancer in Humans?

Dogs are world-class sniffers. Whether working with law enforcement agencies to sniff out drugs and explosives, or zeroing in on that treat you thought was safely hidden in your pocket, our furry friends have a sensational sense of smell.

We use our dogs' all-powerful schnozzes to perform a wide range of important tasks, and this now includes the remarkable job of sniffing out cancer in humans. Following the fascinating results of research around the world, there are now several studies underway to determine whether dogs could potentially be trained to provide early-stage detection of a number of cancers.

So, how and why do dogs smell cancer? Let's give the topic a closer sniff to find out.

Watching a dog that's been professionally trained to smell cancer do its job is an amazing sight. With wagging tails, excited body language, and impressive focus, these dogs look for all the world like they're on a treasure hunt — except finding the treasure could potentially save someone's life.

For the average dog owner, it doesn't take a degree in animal behavior to recognize when your dog is tracking a pretty interesting scent. With nose pressed to the ground or thrust in the air, your dog inhales and exhales rapidly to circulate air into their impressive snout and get to work identifying exactly what it is.

Whatever else is going on around them is usually completely ignored while they zero in on whatever fascinating odor they've detected. This is typically accompanied by a wagging tail and an intense level of focus that practically screams, "I've found an incredibly interesting smell that requires thorough investigation right now! The rest of the world, including you, will just have to wait." 

Professional cancer-sniffing dogs are trained to give some sort of indication when they've found a blood or urine sample, such as sitting next to the offending sample or tapping it with a paw. Check out some of the videos of these dogs in action on YouTube to get a better idea of how they work and the amazing feats they're capable of.

Since the time of Hippocrates, the knowledge that different diseases have unique smells has been widely accepted. These smells are produced by chemicals known as volatile organic compounds, and they're excreted in sweat, urine, breath and other bodily fluids. These compounds create an "odor fingerprint" that can change due to age, gender, diet and, of course, health.

Throughout the second half of the 20th century, there was plenty of anecdotal evidence of dogs alerting their owners that they had cancer. And while cancer volatile organic compounds were first detected in human urine in 1971, it wasn't until 1989 that the idea of using dogs to help diagnose cancer was first suggested.

Writing to medical journal The Lancet, two dermatologists referred to the case of a woman who, due to the high level of attention her dog was paying to a mole on her upper leg, decided to seek a second opinion about what the mole was. Rather than being nothing to worry about, the mole turned out to be a malignant melanoma, a deadly skin cancer, which smelled different to the dog's nose in some way.

Moving into the 21st century, several separate studies have shown that dogs can not only sniff out several types of cancer, but could also potentially provide a highly effective form of early-stage diagnosis.

Some types of cancer, for example, cervical cancer, are quite easy to detect early using screening. Unfortunately, several other forms of cancer are much harder to pick up in their early stages, and often require painful and invasive biopsies for accurate detection. 

These are some of the cancers that dogs could potentially be used to detect earlier than many current methods allow. With dogs capable of sniffing out remarkably small concentrations of odors — we're talking one part per trillion, or a drop of blood in an Olympic-sized swimming pool — there have been numerous studies done around the world to try to determine just how effective our furry friends may be at sniffing out the disease.

• Medical Detection Dogs, a UK charity, has shown that specially trained dogs can detect prostate cancer in urine in 93 percent of cases.
• Researchers at the Humanitas Clinical and Research Centre in Milan trained two German Shepherds to detect the smell of prostate cancer. After five months of training, the two dogs got it right around 98 percent of the time.
• Scientists at the Monell Chemical Senses Centre and the University of ­Pennsylvania are training a team of dogs to detect ovarian cancer, which produces very few symptoms, in samples of blood plasma.
• A 2006 study showed that dogs could be trained to detect cancer based on breath samples. The five dogs detected lung cancer with 99 percent accuracy and breast cancer with 88 per cent accuracy.
  

At the moment, it's still too early to tell just how canine cancer testing will be used, but it's a fascinating area of study and one that shows just how remarkable our furry friends are.

Your dog's sense of smell is thousands of times more powerful than your own, so why not put it to work? Scent training involves teaching your dog to locate a specific odor or object, often in increasingly difficult hiding places, and is a great way for you and your pooch to spend some quality time together. 

The first step is to teach your dog to associate a particular smell with a reward. For example, every time they find the odor they get a treat, lots of cuddles and praise or maybe a play with their favorite toy. 

Once they've got the hang of this, you can start encouraging them to search for hidden odors. You could conceal an object under a cardboard box, for example, or set up a tasty treat treasure hunt around your house. As your dog gets the hang of it, your hiding places can become more elaborate and advanced.

This is an excellent way to put your dog's incredibly powerful sense of smell to use, and most pooches will have a whale of a time searching for the odor they know will bring a reward. Just make sure you keep your training sessions short and sweet to avoid boredom, and that you always have rewards on hand to make the hunt worth your dog's while.