The acute sense of smell that makes dogs useful for detecting illegal substances at airports might also be used to help doctors diagnosis bladder cancer, researchers reported this week in the British Medical Journal.

Carolyn Willis, from Amersham Hospital in the UK and colleagues report a “proof-of-principle” study showing that dogs can be trained to detect bladder cancer by “smelling” urine.

The authors note that bladder tumors produce volatile organic compounds. “Some of these organic compounds are likely to have distinctive odours; even when present in minute quantities, they could be detectable by dogs.”

To test this, they used urine samples from 36 patients with bladder cancer, which were compared with108 samples from diseased and healthy individuals; 63 of the samples were used exclusively in final testing of the dogs.

The authors trained six dogs of different breeds for 7 months to discriminate between urine from patients with bladder cancer and urine from those without cancer. Two dogs were trained with dried urine and the remainder with liquid specimens.

After training, each dog was offered seven urine samples-one bladder cancer sample and six comparison samples from individuals of the same sex. The dogs identified their chosen sample by lying next to it.

Each dog underwent the test nine times. Altogether, the dogs correctly selected bladder cancer urine on 22 out of 54 occasions, an average success rate of 41% compared to 14% expected by chance alone.

“Despite the fact that we had not used dogs with proved scenting abilities, and despite the inclusion of age matched diseased controls, we achieved a statistically significant success rate,” the authors write. “Our study provides the first piece of experimental evidence to show that dogs can detect cancer by olfactory means more successfully than would be expected by chance alone.”

“The results we achieved should provide a benchmark against which future studies can be compared, and it is to be hoped that our approach to training may assist others engaged in similar work.”

Commenting on the paper, statistician Tim Cole from the Institute of Child Health in London notes that the study was carefully designed. “On balance the results are unambiguous,” he writes in an accompanying commentary. “Dogs can be trained to recognise and flag an unusual smell in the urine of bladder cancer patients.”

The urine sample from one comparison subject was consistently identified as positive for bladder cancer by the dogs, he notes. Although cystoscopy and ultrasound results were negative, the consultant tested the subject again-and found a kidney carcinoma.

SOURCE: British Medical Journal. September 24, 2004.