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Dogs Smell Cancer in Patients’ Breath, Study Shows

http://news.nationalgeographic.com/news/2006/01/0112_060112_dog_cancer.html
Stefan Lovgren, for National Geographic News

January 12, 2006

Dogs can detect if someone has cancer just by sniffing the person’s
breath, a new study shows.

Ordinary household dogs with only a few weeks of basic “puppy
training” learned to accurately distinguish between breath samples of
lung- and breast-cancer patients and healthy subjects.

“Our study provides compelling evidence that cancers hidden beneath
the skin can be detected simply by [dogs] examining the odors of a
person’s breath,” said Michael McCulloch, who led the research.

Early detection of cancers greatly improves a patient’s survival
chances, and researchers hope that man’s best friend, the dog, can
become an important tool in early screening.

The new study, slated to appear in the March issue of the journal
Integrative Cancer Therapies, was conducted by the Pine Street
Foundation, a cancer research organization in San Anselmo, California.

Biochemical Markers
Dogs can identify chemical traces in the range of parts per trillion.
Previous studies have confirmed the ability of trained dogs to detect
skin-cancer melanomas by sniffing skin lesions.

Also, some researchers hope to prove dogs can detect prostate cancer
by smelling patients’ urine.

“Canine scent detection of cancer was something that was anecdotally
discussed for decades, but we felt it was appropriate to design a
rigorous study that seriously investigated this topic to better
evaluate its effectiveness,” said Nicholas Broffman, executive
director of the Pine Street Foundation.

Lung- and breast-cancer patients are known to exhale patterns of
biochemical markers in their breath.

“Cancer cells emit different metabolic waste products than normal
cells,” Broffman said. “The differences between these metabolic
products are so great that they can be detected by a dog’s keen sense
of smell, even in the early stages of disease.”

The researchers used a food reward-based method to train five ordinary
household dogs.

Encountering breath samples captured in tubes, the dogs gave a
positive identification of a cancer patient by sitting or lying down
in front of a test station.

By scent alone, the canines identified 55 lung and 31 breast cancer
patients from those of 83 healthy humans.

The results of the study showed that the dogs could detect breast
cancer and lung cancer between 88 and 97 percent of the time.

The high degree of accuracy persisted even after results were adjusted
to take into account whether the lung cancer patients were currently
smokers.

“It did not seem to matter which dog it was or which stage cancer it
was, in terms of our results,” Broffman said.

Different Wiring
According to James Walker, director of the Sensory Research Institute
at Florida State University in Tallahassee, canines’ sense of smell is
generally 10,000 to 100,000 times superior to that of humans.

It is unclear what exactly makes dogs such good smellers, though much
more of the dog brain is devoted to smell than it is in humans.
Canines also have a greater convergence of neurons from the nose to
the brain than humans do.

“The dog’s brain and nose hardware is currently the most sophisticated
odor detection device on the planet,” McCulloch, the study leader,
said. “Technology now has to rise to meet that challenge.”

Researchers envision that dogs could be used in doctors’ offices for
preliminary cancer detection.

“There are lots of experimental treatments,” Walker said. “This could
be an experimental diagnostic tool for a while, and one that is
impossible to hurt anyone with or to mess up their diagnosis with.”

Broffman, the Pine Street director, hopes to build on the current
study to explore the development of an “electronic nose.”

“Such technology would attempt to achieve the precision of the dog’s
nose,” he said. “Such technology would also be more likely to appear
in your doctor’s office.”