Scientists are also using chemical analysis and nanotechnology to try to identify cancer biomarkers in breath, sweat and urine that could be used in blood tests or other tests to detect cancer. If they can identify the chemical changes responsible for the odour the dogs are picking up, it may be possible to develop computerised screening instruments with the same sensitivity dogs have.
There is growing interest in the possibility that dogs, because of their incredible sense of smell, might be able to âsmellâ cancer. The hypothesis was first raised in 1989 when doctors described a case of a woman concerned about a mole that her dog would constantly sniff at and had tried to bite at which turned out to be a malignant melanoma.Â
There have been only a few studies with small numbers of patients, but the results suggest dogs could be trained to detect these compounds. Studies over the past decade have shown trained dogs could identify the urine of patients with bladder cancer almost three times more often than would be expected by chance alone, detect lung cancer in exhaled breath samples with very high accuracy (in two separate studies) and identify ovarian and colorectal cancers by smelling breath samples.Â
There have been several other reports since then of dogs detecting cancers by constantly sniffing or nudging an area of their ownerâs body. Tumours produce volatile organic compounds, which are released into urine, exhaled breath and sweat. Even in minute quantities these compounds are thought to have a distinct odour, particularly in the early stages of cancer when cells are dividing.Â
How Do Dogs Act When They Smell Cancer?
“The ability of dogs to detect melanoma, a potentially fatal skin cancer, has been formally studied and confirmed,” says Ashley Stenzel, PhD, a Roswell Park postdoctoral fellow. Dr. Stenzel notes that in case studies, dogs persistently sniffed, licked and nipped at melanoma lesions on their owners’ skin, even through clothing, prompting the owners to identify the cancerous sites and seek care from clinicians. “Given that melanoma is a cancer presenting with lesions on the skin, it would be logical for dogs to be able to detect a lesion,” Dr. Stenzel says. “However, the use of canine olfactory detection has also been studied in other examples of cancer.”
Lauren credits her dog, Victoria, for calling attention to a bump on her nose, which turned out to be basal cell carcinoma.
In one widely noted anecdotal case, Lauren Gauthier, founder of Magics Mission hound rescue organization, reported that Victoria, her adopted Treeing Walker Hound, “persistently sniffed and stared at what seemed like a pimple on my right nostril. It was so odd and she was so persistent that I finally decided to have it checked out.” The “bump” ended up being basal cell carcinoma, a common type of skin cancer. “As soon as I had Mohs surgery to remove the cancer, Victoria’s strange behavior stopped.”
Claire Guest, MSc, DHP, BCAh, CEO of Medical Detection Dogs, recalls that Daisy, her Fox Red Labrador, who is trained to sniff out cancer in the lab, kept staring and pawing at her chest. While trying to decipher Daisy’s behavior, Dr. Guest discovered a lump that turned out to be a malignant tumor deep in her breast.
In Being a Dog, Horowitz describes a Dachshund puppy that repeatedly sniffed her owner’s armpit. Eventually the woman found a lump in her armpit, leading to a breast cancer diagnosis.
How Do Dogs Act When they Smell Cancer?
There are numerous reports of individual experiences regarding dogs directing attention to suspicious lesions, bumps, or moles that turn out to be cancerous. In these reports, the dog will:
In many cases, the persistent behavior of the dog eventually pushes the individual to seek medical attention resulting in a formal diagnosis and treatment plan.
Dogs Can Smell Cancer | Secret Life of Dogs | BBC Earth
Dogs can be trained to be cancer-sniffing wizards, using their sensitive noses to detect cancerous fumes wafting from diseased cells. This sniffing is noninvasive and could help diagnose countless people, which begs the question: If these pups are so olfactorily astute, why arent they screening people for cancer right now?
Heres the short answer: Dogs do well in engaging situations, such as helping law enforcement track scents or guiding search-and-rescue teams in disaster areas. But sniffing thousands of samples in which only a handful may be cancerous is challenging work with little positive reinforcement.
Moreover, it takes time and energy to train these pups, who, despite extensive preparation, still might miss a diagnosis if theyre having a bad day, experts told Live Science. [20 Weird Dog and Cat Behaviors Explained by Science]
But thats not to say that dogs cant be helpful in the development of manmade screening tools that “smell” cancer. Its known that cancerous cells emit unique odors, but scientists have yet to identify the specific compounds responsible for these scents.
One way dogs might be able to help pinpoint cancer-specific odors is to give the dogs certain cancerous samples to sniff, and then slowly remove compounds from the sample. If the dog stops responding to the sample after several components are removed, “then you know youve taken out that component of the mixture that is specific to the cancer,” said Dr. Hilary Brodie, a professor in the Department of Otolaryngology at the University of California, Davis. Researchers could then analyze these individual components and develop biochemical tests that could reliably screen patients, he said.
“Theres lots that the dogs can do, but I dont think wholesale screening of the population is where its heading,” Brodie told Live Science.
In 1989, the British journal The Lancet published the first dog-sniffing-out-cancer report. In a letter to the editor, two dermatologists described how a dog reportedly spent several minutes each day sniffing a colored lesion on its owners thigh, and even tried to bite off the spot when she wore shorts. Concerned, the woman had doctors inspect the lesion, which turned out to be a malignant melanoma.
“This dog may have saved her owners life by prompting her to seek treatment when the lesion was still at a thin and curable stage,” the doctors wrote in the letter.
Other reports of dogs detecting malignant melanomas followed, but it wasnt until 2006 that high-quality, double-blinded studies were published, said Dr. Klaus Hackner, a pulmonary physician at Krems University Hospital, in Austria. (In the double-blinded studies, neither the dogs nor their handlers knew which samples were cancerous.)
Soon, there were countless studies showing that trained dogs could detect specific cancers by sniffing biological samples, such as a persons breath or urine. Thats because cells, even cancerous ones, give off volatile organic compounds (VOCs). Each type of cancer likely has a distinct VOC, meaning it has a different odor compared with other cells, Hackner said.
Given that dogs have more than 220 million smell receptors in their noses, theyre excellent animals for sniffing out disease, Hackner said. In comparison, humans have a “mere” 5 million smell receptors in their noses, he said. [Why Do Dogs Have Whiskers?]
Most dogs can be trained to recognize the odor of a specific cancer in about 6 months, Hackner said. However, many studies had setups that work in laboratories, but not the real world: often, the dog would be given five samples that always had one cancerous specimen. In reality, depending on the type of cancer, a sniffer dog might find just four cancerous specimens out of a batch of 1,000, he said.
If neither the dog nor the handler knows which four out of those 1,000 samples are cancerous, the handler cant give the dog positive reinforcement when the dog picks the right specimen, Hackner said.
“I think this was one main point for why our study failed,” said Hackner, whose 2016 work, which had a real-world-like setup, was published in the Journal of Breath Research. “We were not able to provide positive feedback because neither one knew in the screening situation if the dog was right or not. This was stressful for both the dogs and the handlers.”
This situation could be remedied if there was always a planted cancerous sample in each set, so the dog could get a reward and wouldnt be bored after sniffing thousands of noncancerous samples from patients, he said.
But even if the setup could be changed to accommodate the dogs, it wouldnt be a realistic way to screen patients, Brodie said. It would take an immense amount of resources to train dogs to recognize the many types of cancer that can affect humans. In addition, while no test is perfect, at least doctors know how accurate different tests, such as mammograms, are, and at what rate they produce false positives and false negatives. But these rates would vary for each dog, Brodie said.
Moreover, dogs can get bored, hungry and “have bad days, just like you and I,” Brodie said. “Youd have to be carefully monitoring their effectiveness throughout their cycles.”
Rather, Brodie and Hackner envision dogs helping researchers create and refine biochemical “nose” machines, known as e-noses, that could “sniff” patients and deliver diagnoses, they said. These machines already exist for certain medical conditions, but could be made more sensitive and applicable to more diseases with the help of dogs, Brodie said. But the research isnt there yet, he noted.
In one project, Brodie and his colleagues were studying whether dogs could detect volatile organic compounds from head and neck cancer patients by smelling the breath patients had exhaled into a container. But the researchers put the project on hold after the dog trainer began broadcasting that her dogs could sniff out cancer.
“We didnt want to be affiliated with that,” Brodie said. “We wanted to prove that theyre detecting it, not state that theyre detecting it and then prove it. Youve got to do the science first. This is not even close to or near prime time.”
Laura is the archaeology/history and Lifes Little Mysteries editor at Live Science. She also reports on general science, including archaeology and paleontology. Her work has appeared in The New York Times, Scholastic, Popular Science and Spectrum, a site on autism research. She has won multiple awards from the Society of Professional Journalists and the Washington Newspaper Publishers Association for her reporting at a weekly newspaper near Seattle. Laura holds a bachelors degree in English literature and psychology from Washington University in St. Louis and a masters degree in science writing from NYU.