for National Geographic News
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.
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.