Doctor dog

Researchers at the relatively unknown non-profit Pine Street Foundation in Northern California claim they have trained dogs to identify patients with breast or lung cancer -- based on the smell of their breath – with near perfect accuracy.

The study was based upon concepts established in the 1980s, specifically that tumours exude small amounts of alkanes and benzene derivatives not present in healthy tissue. Because cancer cells release molecules different from those of their healthy counterparts, researchers sought to discover if these differences could be perceived by the famously sensitive canine nose.

A dog's nose has long been considered by dog trainers and chemists alike to be one of the world's most powerful olfactory sensors. Previous research has shown that dogs, whose noses can pick up scents in the low parts-per-billion range, can be trained to detect skin cancers or bladder cancer from a patient's urine. But never before has it been done with such accuracy.

After more than 12,000 separate dog/breath sample interactions, researchers said the dogs identified 99 per cent of lung cancer breath samples, including early stage cancer patients, and 88 per cent of the breast cancer samples. Accuracy did not vary greatly by cancer stage or by dog. Nor was the dog's diagnostic performance affected by the patient's age, tendency for smoking, or most recently eaten meal.

Researchers say these diagnoses rival those from CT scans, PET scans, X-rays, and mammograms.

But is the near-perfection of the dogs' performance too good to be true?

Experts who read the study could not find any obvious fatal flaws in the methodology, and that dogs might be able to detect cancer is "not crazy at all," Dr. Ted Gansler, director of medical content in health information for the American Cancer Society told The New York Times. "It's biologically plausible," he said, "but there has to be a lot more study and confirmation of effectiveness."