A Collie-Doberman mix won’t stop sniffing at a mole on the arm of its owner and even resorts to trying to bite it off. The alarmed woman contacts her doctor who affirms the worried dog’s behavior. The mole is indeed cancerous.

These stories, among at least 16 verifiable anecdotes about dogs detecting cancer in their unsuspecting owners, prompted researchers in England in 2004 to test whether dogs could be trained to detect bladder cancer. The results, while statistically unimpressive, were enough to warrant further studies.

In 2006, an international collaboration of scientists at the Pine Street Foundation conducted a study using five dogs to see if they could detect breast and lung cancers. Unlike the bladder cancer study in which dogs sniffed patients’ urine samples, breath samples were used because it was thought the biomarkers of cancer would be easier to identify in breath samples. Researchers were successful in teaching dogs to identify both breast and lung cancers.

“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, lead researcher at the Pine Street Foundation, a cancer research organization in San Anselmo, California.

It’s been theorized that cancer cells emit different metabolic waste than normal cells. The differences between these wastes are significant enough that they can be detected by a dog’s amazing olfactory abilities, even in the early stages of disease.

The dogs sniffed test tube breath samples of cancer patients and healthy controls. The test tubes contained fiber to capture microscopic particles. The dogs were trained using clickers, praise and food rewards to sit or lie down in front of a positive cancer sample. “We think dogs are like people and perform best when they get positive feedback,” says McCulloch.

Once trained, the results were remarkable: dogs achieved an accuracy rate of 88% for breast cancer and 99% for lung cancer, much better than laboratory tests. During the actual trial phase to ensure that dogs were not picking up on subtle clues from the humans, the researchers in the room with the dogs did not know which test tubes contained the cancerous samples.

Buoyed by the results, Pine Street researchers are now working with the dogs to see if they can detect ovarian cancer, which often evades detection yet is far more treatable when caught in the early stages.

So, what’s next for man (and woman’s best friend)? Will your health screening someday include being sniffed over by a Golden Retriever? Well, maybe not. But being able to use breath samples to detect cancers in their earliest stages is important not only for savings lives, but being able to treat cancer with less invasive methods.

As McCulloch notes “The fact that it was dogs is almost beside the point. Although I should add that the dogs performed so well that now technology really has to rise to the challenge that they laid down.”