How does your dog smell? Olfactory detection of human bladder cancer

Anecdotal evidence has shown that dogs, with their acute sense of smell, might be able to detect cancers in humans by picking up the odour given off by the cancer cells. In the past 15 years, two letters have been published in the Lancet, seemingly describing dogs’ ability to predict the presence of cancer later diagnosed by a doctor. Alongside the anecdotes, good theoretical evidence indicates that dogs at least ought to have such capabilities, because we already know that tumours release volatile organic compounds (or scent chemicals) into the air. Although these compounds are too faint for humans to detect, they could well be within the range of a dog’s olfactory (sense of smell) capabilities. In addition to the theoretical benefits, a clinical motive for investigating the possibility of using dogs to diagnose cancer exists, because interest in volatile compounds as indicators of cancer is growing elsewhere in medicine. The purpose of this study was to test, under rigorous experimental conditions, the idea that dogs might be able to detect cancer through their sense of smell.