It’s no secret that dogs can tell when something is bothering their
humans. But now it’s been determined that they can tell when things are
off with our bodies as well. New studies show that diseases give off
odors that dog’s noses are strong enough to smell, and with a little
training they can determine who is sick and who is not. Read on to see
if man’s best friend will become a tool for early detection of disease.
It’s hard to imagine how dogs experience
the world, because so much of it is accessed through their snouts. Dogs
live in an olfactory world, full of smells that tell complex stories.
They detect odors direct from the source as well as residual odors that
persist in an area long after the source has left.
Dogs are born sniffers. Humans have roughly five million olfactory
cells in their noses. It sounds impressive, until you compare it to the
200 million cells in a typical dog’s nose. Canines’ sense of smell is
generally 10,000-100,000 times superior to that of humans. Much more of
their brains are devoted to processing smell, and they also possess
more genes that code for olfactory ability and many more olfactory
neurons than humans.
People have known about and taken advantage of dogs’ sense of smell
for centuries, even breeding some dogs to be scent hounds used in
tracking and hunting. In recent years, dogs have been trained to sniff
out explosives, drugs, bodies and other scents.
Anecdotes about dogs “sensing” when their owners were sick before any
diagnosis was made may sound crazy at first. But in the last decade,
several scientists have put dogs’ noses to the test in controlled
laboratory experiments — diseases give off odors that, at least
theoretically, dogs can smell. Malignant tumors exude tiny amounts of
chemicals called alkanes and benzene derivatives not present in healthy
tissue. If a dog can identify chemical traces in the range of parts per
trillion, is it really crazy to think they can detect cancer, even
before people know they’re sick?
The first scientific test of canine
cancer-detecting, to my knowledge, was in 2004. James C. Walker, of the
Sensory Research Institute at Florida State University, and
colleagues trained two dogs to detect melanoma tissue samples hidden on
the skin of healthy volunteers. The dogs were trained and tested with
methods normally used for forensic bomb- or drug-sniffing dogs. One dog
“confirmed” the presence of melanoma on five patients, and even detected
cancer in a sample that was initially deemed negative, but subsequent
histopathological examination revealed to contain melanoma in a fraction
of the cells.
A 2006 study by the Pine Street Foundation,
a cancer research organization in San Anselmo, Calif., used more dogs
and samples for even more robust results. The researchers selected three
Labrador retrievers and two Portuguese water dogs with no prior
training. Lung and breast cancer patients breathed into tubes which
captured samples of their breath. The dogs then underwent several weeks
of training with the samples. For testing, the researchers used a new
batch of breath samples. The dogs correctly detected 99 percent of the
lung cancer samples, and made a mistake with only 1 percent of the
healthy controls. With breast cancer, the dogs identified positive
samples 88 percent of the time with no false positives. The dogs
performed as well as the most recent screening tests for the diseases.
It is important to note that all the tests were double-blind, meaning
neither the dog handlers nor the experimenters knew which samples were
which. By the scent of breath samples alone, the dogs identified 55 lung
and 31 breast cancer patients as well as 83 healthy people.
Scientists again trained dogs to sniff out
lung cancer in a more recent study published in 2011. A group of German
researchers wanted to know if dogs could discriminate between breath
samples from lung cancer patients, chronic obstructive pulmonary disease
(COPD) patients, and healthy volunteers, and whether the presence of
tobacco in the samples made a difference. The dogs correctly identified
71 samples with lung cancer out of 100. They also successfully detected
372 samples that did not have lung cancer out of 400. It seemed the dogs
were able to detect lung cancer independently from COPD and tobacco
smoke.
A 2004 study in which dogs were trained to
detect bladder cancer in humans by smelling their urine had a smaller
success rate, but is notable for an unexpected result. Carolyn M. Willis
of Amersham Hospital in Great Britain and colleagues trained six dogs.
One dog failed completely, but two picked out the positive samples 60
percent of the time. The surprise came when one of the non-cancerous
control samples caught the interest of the dogs. The medical staff
assured the disappointed trainers that the sample was from a healthy
person, but because the dogs consistently identified this sample as
“positive,” it was sent back to the hospital for further tests. On
re-examination the person was found to have cancer on his kidney and
bladder cancer. The dogs caught it before anyone else.
In a 2011 study from Japan, a Labrador
retriever trained to sniff out colorectal cancer was at least 95 percent
as accurate as a colonoscopy when smelling breath samples and 98
percent correct with stool samples. The dog was especially effective at
detecting early-stage cancer and could also discern polyps from
malignancies, which a colonoscopy cannot do.
Studies like these are fascinating for what
they tell us about dogs’ keen sense of smell, but medical professionals
also see practical and technological implications. Dogs’ noses are
inspiring a race between scientists to create an artificial sniffer with
similar acuity for quick and easy use in hospital laboratories — this
involves precisely identifying the compounds dogs are picking up on in
the samples from cancer patients.
Early detection is paramount in many
cancer treatments. For some diseases, like prostate cancer, the blood
tests currently used are notoriously inaccurate. Could man’s best friend
become a tool in early screening? Whether actual dogs will be making
future diagnoses is uncertain, but it is clear they possess a pretty
powerful tool we are only beginning to understand and appreciate.
This
incident is believed to have happened when Atkinson was on a family
holiday in Kenya, while he was traveling in a Cessna 202 private
airplane along with his wife Sunetra, and two children, Ben and Lilly. 
