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Reviewed for accuracy on March 19, 2019, by Dr. Katie Grzyb, DVM

Doctors and researchers are getting better all the time at detecting and treating all kinds of diseases, conditions and ailments. And over the years, they’ve gotten an assist from an unlikely ally—sniffer dogs!

Research has shown that dogs’ high-powered noses have the capability to literally sniff out diseases—most notably cancers such as bladder cancer, prostate cancer, ovarian cancer and lung cancer.

Dr. Jennifer Essler, a postdoctoral fellow who is working on detection research at the Penn Vet Working Dog Center in Philadelphia, also trains dogs to detect ovarian cancer. She says that while she’s not sure if “the sky’s the limit, it seems like dogs can detect [the cancers] we’ve thrown at them so far!”

But how can dogs smell disease? How do you train cancer-sniffing dogs to alert researchers? And what are the practical applications of dogs that can smell cancer?

How Can Dogs Smell Disease?

Basically, dogs have super noses. “Dog noses have up to 300 million smell receptors. Human noses only have five million,” says Dr. Ann Hohenhaus, a staff doctor at NYC’s Animal Medical Center.

She adds that dogs’ brains are wired to be super-attuned to smell. “Dogs can differentiate between 30,000-100,000 different smells. Humans can only differentiate between 4,000-10,000, to put that in perspective.”

However, despite knowing how powerful dogs’ noses are, experts aren’t exactly sure what the dogs are smelling when they detect cancer. Dr. Essler says, “It could be anything at this point, from a chemical change—the body’s response to cancer—to something from the actual tumor in the blood. We aren’t sure; we just know that something smells different.”

She adds, “Dogs trained on tumor samples were readily able to recognize patient’s blood samples, so we suspect it has something to do with the tumor itself.”

How Sniffer Dogs Are Trained to Detect Cancer

So does that mean any dog can be a sniffer dog? Not quite. Dr. Essler says that while all dogs have disease-detecting capabilities, the training is much more personality-focused than breed-specific. 

“We’ve had a good mix of dogs go through our program, including Shepherds, Spaniels and Labs. Breed isn’t important, but the dog has to be motivated to distinguish between similar odors and calm enough to perform this consistently. We’ve had dogs enter the program and sniff through everything super, super quickly, and they aren’t well-suited to this type of work.”

Dogs who begin training to detect cancer have already been through a rigorous scent-detection training process. “By the time they get to us, they just need to learn a new odor—cancer—and how to distinguish it from other odors,” says Dr. Essler.

Training for sniffer dogs in Dr. Essler’s program involves learning how to detect cancer in an eight-port wheel, with each port offering up a different scent.

“First, we train the dogs to find the malignant cancer odor. Then we introduce normal [tumor-free] human odor and then benign tumor odors and require the dogs to differentiate between them all. Once they get good at that, we introduce other scents that they might encounter in a medical environment, like saline, rubber gloves and paper towels,” she explains.

“Normal, tumor-free human scent,” as well as the scent of different cancers, is isolated through a process called gas chromatography mass spectrometry analysis. “This isolates and identifies the chemical compounds emitted from plasma of the various groups—cancer, benign tumor and healthy control,” explains Leslie Stein, director of communications for the Monell Chemical Senses Center in Philadelphia, the world’s only independent, nonprofit scientific institute dedicated to basic research on taste and smell. The Monell Center provides the Penn Vet Working Dog Center with its odor samples.

All of the scent training is done remotely via video, with Dr. Essler and her colleagues outside the room, so that the dogs don’t pick up on any subconscious clues and learn how to cheat the system. “We use a clicker to tell them whether they’re right,” she adds.

Dogs that don’t end up as cancer-detection dogs may become police dogs that search for drugs or even search-and-rescue dogs.

Practical Applications for Cancer-Sniffing Dogs

Dr. Essler says that the end goal isn’t having dogs act as diagnosis tools. “They are animals, and they have good days and bad days, so we can’t necessarily rely on them like we could a laboratory test. But, these dogs do have a special skill and can be very impactful in the right environment,” she says.

In Dr. Essler’s case, the team at the Penn Vet Working Dog Center is using information gleaned from the dogs’ abilities to develop technology that can detect cancer. “We are using the dogs as our gold standard. They are helping confirm that the electronic device is identifying samples that the dogs have identified as cancer. We are hoping that [our research results in] an ‘electronic nose’ that does what the dogs’ noses do, just electronically,” she explains.

“We never aim to have dogs themselves involved in diagnoses. That is why we are aiming to see what the dogs are recognizing when they distinguish certain odors—so we can make the device as effective as possible and able to screen hundreds of thousands of samples,” Dr. Essler says.

“Diseases aren’t going anywhere, and the applications for a disease-sniffing dog are very open-ended.”

By: Kate Hughes

Featured Image: Laughing_Dog_Photography

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