Dogs have long been called “man’s best friend.” Now, there may be a new reason to honor them with that distinction. A number of studies point to dogs’ uncanny ability to detect cancer.
But how reliable is canine cancer detection? And how early can dogs detect it? Let’s take a closer look at the fascinating research.
Dogs, of course, have much better noses than humans. Dogs use their noses constantly – they sniff everything…food, people, animals, even cuts and sores.
When you enter a room, you scan it with your eyes in a split second. Dogs “see” what’s happening using their noses. You see a cat; they smell a cat. You see a cut; they smell a cut…
Their ability to detect scents is extraordinary. They have:
- Up to 170 cm of specialized tissue inside their nose (their olfactory epithelium); our noses have just 10 cm.1
- Approximately 300 million olfactory receptors. We have five to six million.2
- The ability to “sort” air into two different streams – one for respiration and one for smelling.
- A scent-detection center in their brain that’s 40 times larger than ours.3
All in all, dogs’ sense of smell is 1,000 to 100,000 times stronger than ours.4
Scientists use this analogy to give us perspective: If we were talking about the sense of sight rather than smell, then your dog would be able to see 3,000 miles away what you can see a third of a mile away.
Dozens of cases of dogs detecting cancer
The first published account of dogs’ ability to sniff out cancer came in 1989, when a Border Collie-Doberman mix spontaneously and continually sniffed at his owner’s left thigh. Soon after, doctors diagnosed the owner with malignant melanoma.5
Dozens, if not hundreds, of equally bizarre cases have been reported…
- The dog belonging to a 40-year-old Minnesota woman started nosing her left side and acting oddly. After removing the slobber, she felt a lump, got it checked out, and was subsequently diagnosed with breast cancer.
- A New York woman’s dog persistently sniffed at a red spot on her nose, prompting her to see her doctor. That spot turned out to be basal cell carcinoma.
- The dog belonging to a UK teacher was unusually interested in his owner’s breath. Soon afterwards, the owner was diagnosed with lung cancer.
- A 66-year-old man’s Labrador retriever repeatedly sniffed his owner’s leg through his pants. The man was later diagnosed with basal cell carcinoma.6
- A Wisconsin woman was diagnosed with a benign ovarian cyst, given medication and sent home. But her husky repeatedly sniffed the woman’s belly, which the woman dismissed… until she found her dog hiding in the back of a closet. She was soon diagnosed with stage 3 ovarian cancer. After treatment her dog returned to normal – till two years later when the pet again hid in the back of the closet. Her cancer had returned. Since then the husky has forewarned her of cancer two more times, early enough that it didn’t show on scans.
The stories are remarkable. But do these accounts have any merit?
Research shows the answer is yes…
What we’ve learned from 15 years of research
Years after dozens of reports of dogs spontaneously detecting cancer in people, scientists finally began to investigate.
As part of this investigation, scientists trained dogs to smell cancer. Some dogs were household pets, while others had prior training for explosive detection or to perform other specialized jobs. The dogs’ ages varied.
Over fifteen years of research, dogs accurately identified melanoma, bladder cancer, lung cancer, breast cancer, ovarian carcinoma, prostate cancer, colorectal cancer, hepatocellular carcinoma, and more.7,8,9,10,11,12,13,14,15,16
Even more impressive, the dogs detected cancer with amazing accuracy, sensitivity, and specificity– in some cases close to 100 percent.
In medical testing, sensitivity is the ability to correctly identify those with the disease, the true positive rate. Specificity is the ability to rightly identify those without the disease, the true negative rate.
If doctors could detect cancer early using something as noninvasive, benign, affordable and accurate as a dog’s nose, patients could more easily consider treatment options beyond the conventional ones.
Also, it’s a well-known medical fact that early cancer diagnosis results in a better prognosis and higher survival rate for almost all cancers. And unlike other diagnostics – such as colonoscopies, mammograms, and biopsies – canine cancer detection isn’t invasive and won’t spread cancer.
Odor as an indicator of disease isn’t as far-fetched as you might think, either.
Why ailing bodies give off odor
Doctors in centuries past smelled patients in an effort to detect odors associated with various diseases. Unfortunately, the body odors were usually undetectable until very late in the progression of the disease.
A recent example: An international flight made an emergency landing after passengers complained of a man’s unbearable body odor. Airline officials asked the man to get off the plane, and the story made headlines around the world.
One month later, the man died from a tissue disease called necrosis. Necrosis is the death of body tissue that results from lack of blood flow caused by injury or radiation.17
While this is an extreme case, it proves the point that disease and infection affect body odor. That’s because they change your internal composition.
Researchers studied cancer specifically and found metabolic changes during cancer can spawn new or abnormal volatile organic compounds (VOCs), which serve as cancer biomarkers. Cancer cells are more metabolically active than healthy cells, emitting specific VOCs. Dogs can apparently pick that up in a sick person’s breath, sweat, or other body fluids.
Interestingly, a 2018 study found that dogs were able to detect the VOC sarcosine, a by-product of amino acid synthesis. Levels of this compound rise during the early stages of prostate cancer, making it an ideal diagnostic tool.18
While this study didn’t actually prove that dogs smell sarcosine in their owners or in urine samples, it’s an exciting development in the quest for earlier cancer detection.
Does this make dogs in lab coats the wave of the future?
While dogs in lab coats would undoubtedly be adorable and likely to lower stress levels, that probably isn’t where the science is heading.
First of all, training these “bio-detection dogs” is incredibly expensive and time-intensive. It can cost upwards of $25,000 per dog. One reason is that dogs who sniff out drugs and bombs look for just a handful of scents, but the scent of cancer involves thousands of organic particles dogs must be trained to identify and detect. It’s not exactly an easy task.
Plus, like people, dogs have bad days when they’re tired, bored, distracted, or don’t feel well. In addition, there may be liability issues involved. Who’d be held responsible for a false positive or false negative?
Finally, “dog fakers” may put people’s health at risk by collecting high fees for dogs that aren’t adequately trained for bio-detection. Normal dog trainers are ill equipped to provide the training or certification needed for expert medical diagnosis.
What’s more likely is a device inspired by the animals.
The electronic version of a dog’s nose
It’s worth noting that the DEA and military are already using an electronic version of a dog’s nose for detecting drugs and bombs. And it works! Electronic noses are also currently used as biosensors, too. They “smell” VOCs to detect cancer – and other diseases and disease biomarkers.
While not readily available everywhere, they no doubt are the wave of the future.
Here’s the bottom line today…
Listen to your dog
If you have a dog, and he or she is fixated on a spot, lesion, or body location – or exhibits other repeated odd behaviors – don’t ignore it. Get yourself checked out by a medical practitioner. Maybe your doctor will use an electronic “nose” – more likely not. The science is still developing. But he or she has other diagnostic tools to help decide if your dog is onto something.
Your dog could save your life by warning you about a life-threatening condition. Don’t take that lightly!
- Williams H, Pembroke A. Sniffer dogs in the melanoma clinic? Lancet 1989;1:734
- Williams H, Pembroke A. Sniffer dogs in the melanoma clinic? Lancet 1989;1:734
- Church J, Williams H. Another sniffer dog for the clinic? Lancet 2001;358:930.
- Pickel DP, Manucy GP, Walker DB, et al. Evidence for cancer olfactory detection of melanoma. Appl AnimBehav Sci 2004;89:107-116
- Willis CM, Church SM, Guest CM, et al. Olfactory detection of human bladder cancer by dogs: Proof of principle study. BMJ 2004;329:712
- McCulloch M, Jezierski T, Broffman M, et al. Diagnostic accuracy of canine scent detection in early- and late-stage lung and breast cancer. Int Cancer
- Horvath G, Jarverud S, Horvath I. Human ovarian carcinomas detected by specific odor. In-tegr Cancer Ther 7(2):76-80
- Horvath G, Anderson H, Paulsson G. Characteristic odor in the blood reveals ovarian carcinoma. BMC Cancer 2010;10:643
- Cornu JN, Cancel-Tassin G, Ondet V, et al. Olfactory detection of prostatic cancer by dogs sniffing urine: a step forward in early diagnosis. Eur Urol
- Sonada H, Kohnoe S, Yamazato T, et al. Colorectal cancer screening with odour material by canine scent detection. Gut 2011;60(6):814-819
- McCulloch M, Turner K, Broffman M. Lung cancer detection by canine scent: will there be a lab in the lab. European Resp J 2012;39(3):511-512
- Taverna G, Tidu L, Grizzi F, et al. Olfactory system of highly trained dogs detects prostate cancer in urine samples. J Urol 2015;193(4):1382-1387
- Kitiyakara T, Redmond S, Unwanatham N, et al. The detection of hepatocellular (HCC) from patient’s breath using canine scent detection: a proof-of-con