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Greyhound Nose

The nose knows! We all know dogs possess incredible powers of smell. They sniff out drugs, firearms, and explosives. Some have even been trained to sniff out diseases like diabetes and COVID, as well as cancers. But exactly how is this superpower being put into use by cancer research centers and healthcare providers around the country?

How Do Dogs Detect Cancer?

Studies of dogs and cancer detection indicate that cancerous cells release different metabolic waste products compared to healthy cells in the human body. The difference in smell is so significant that the dogs are able to detect it even in the early stages of cancer. Dogs are able to identify the chemical traces in the range of parts per trillion. They detect some substances in very low concentrations which makes their noses sensitive enough to detect cancer markers in a person’s breath, urine, and blood.

Super Sniffers

It’s no accident that dogs have larger noses than humans. Dog noses have up to 300 million scent receptors, whereas people have ~5 million. So it is no surprise that their olfactory anatomy is much more complicated than ours. Dogs have an olfactory shelf or recess that is separated from the respiratory section. This allows odors to accumulate and be held for recognition even while air is exhaled. Because their smelling ability is not interrupted by air exit, dogs can sniff more or less continuously.

Dogs can detect odor signatures of disease and, with training, alert people to their presence. People refer to dogs that undergo training to detect certain diseases as medical detection dogs. The dogs do not sniff the people directly, but rather samples are presented to the dog. Some samples are controls, meaning the sample was taken from a healthy person who does not have cancer. Other samples are taken from individuals who the medical team suspect may have cancer. The dog identifies the positive sample by sitting by or nudging the sample. These dogs are not the primary method used to screen cancer, but used in conjunction with traditional screening methods.

Some cancers, such as prostate cancer, are particularly hard to diagnose. State of the art diagnostic tests return many false positives. Dogs have been found to be over 90% accurate alerting to prostate cancer. In these cases, the dog’s reaction, along with test results, are combined to form the diagnosis.

Medical detection dogs have also been trained to detect chemicals that indicate bladder cancer in urine samples, lung and breast cancer in breath samples, and ovarian cancer in blood samples, to name just a few. Some studies have confirmed the ability of trained dogs to detect the skin cancer melanoma by just sniffing the skin lesions.

The fact that dogs can detect cancer has significant benefits for humans. Using dogs to detect and diagnose cancer is a low-risk, noninvasive method. Medical detection dogs present few side effects and may offer advantages because they are mobile, can begin work quickly, and can trace an odor to its source.

They also have the potential for use in patient care settings or laboratories to identify cancer in tissue samples from people with suspected cancers.

Greyhound Nose

So Why Do They Care?

The answer is simple: if something is wrong with us, this will affect the dog. If we are sick, this could directly affect our ability to provide food and shelter for the dog. The dog “notices” small changes which could signify that we are in trouble. They notice something different that’s not like the rest of us. This “sick scent” is a small change but can mean that we may become incapacitated in some way, which means the dog may suffer. The sick scent is very important for the dogs’ (and mans) survival, as smelling disease helps the dog catch his own prey, as well as larger prey for man.

How Do Dogs Alert to the Presence of Cancer?

It’s often reported that dogs detect breast cancer in their humans far before the human knew there was a problem. Some dogs have been reported to try to lick the area or nudge it with their noses. In most cases, the dog sniffs, scratches or nudges at the affected area persistently, as if trying to alert their human companion to something.

I personally had an experience where I had a bump on the top of one knee, which looked to me like a pink blister, about the size of a pencil eraser tip. It was summer and I was visiting a friend, sitting on the sofa. I was wearing shorts, and her Scottie jumped up in my lap, and tried to bite off that little bump! I was so surprised, and I laughed as he jumped down and went about his business.  Later though, I was thinking about it and the next time I saw my primary care doctor, I had him remove it. He was pretty sure it was nothing, but sent it for a biopsy.  Sure enough, it was a rare form of cancer (syringomatous carcinoma)!

One man’s dog licked behind the man’s ear, and it turned out to be a melanoma lesion.  A woman’s dog buried her snout into her owner’s chest and was pawing at her anxiously when she detected cancerous cells in her lungs.

Stories like this show that there isn't one single way dogs will react to the smell of cancer, as much of their reaction will be based on their individual temperaments and training. But the one thing dogs in all cases had in common was a distinct change in their normal behavior that indicated to their pet parents that something was off. If you notice a change in your dog's behavior, that doesn't necessarily mean there is anything to be concerned about; however, consistent patterns could be worth exploring. If a visit to the veterinarian shows that your pooch is healthy but their behavior continues, it may be worth scheduling a visit to your doctor as well.

Can Technology Compete With a Dog’s Nose?

Some scientists have tried to develop breathalyzer-type tests to detect the same smells the dogs pick up, but no machinery has proven to be as successful as the dogs’ noses so far. Traditionally, hunting dogs and police dogs are trained in cancer sniffing, since these working dogs are known to have keen senses of smell and high obedience levels, but The Working Dog Center in Philadelphia trains other dog breeds as well. It seems that nearly any breed of dog can smell cancer; the trick is teaching them to recognize and report it.

“We don’t ever anticipate our dogs walking through a clinic,” said the veterinarian Dr. Cindy Otto, the founder and executive director of the Working Dog Center. “But we do hope that they will help refine chemical and nanosensing techniques for cancer detection.”

There is ongoing research into what we can learn from looking at the dog’s nose, and some researchers are developing electronic noses that may one day do a job similar to medical detection dogs.

One path of further research is using canine scent detection as a screening method for cancers, and the other would be to determine the biologic compounds the dogs detect and then design cancer-screening tests based on those compounds.  Working with the dogs in the lab, some researchers are striving toward finding the exact chemical components that give cancer its unique smell, so handheld detectors can be developed and widely utilized in the healthcare setting.

For many cancers, there is currently no screening method available at all: people don’t know they’re suffering from the disease until they start to experience symptoms. And no variety of cancer currently has a reliable screening method for the disease in its earliest stages. This means that someday in the not-too-distant future, dogs’ noses will be saving many thousands of lives, whether it’s through a mechanical nose or a real, live four-legged friend.

And that's not so crazy — after all, dogs have long been known to be able to read humans in unparalleled ways. Their highly attuned senses alert them when we are sad or sick, and they often act as partners to help alert us to danger. It's just one more incredible demonstration of the powerful bond between humans and our canine best friends.



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