Dogs Smell Cancer in Patients' Breath, Study Shows

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."

Free E-Mail News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).


© 1996-2008 National Geographic Society. All rights reserved.