Dogs can be trained to sniff out a tell-tale scent of bladder cancer from urine, early experimental results suggest.

The canine's keen sense of smell allows them to identify those with bladder cancer compared to people with other urological diseases or healthy controls.

For the "proof of principle" study, volunteers from the British charity Hearing Dogs for Deaf People trained six of their pets for seven months. The canines were deliberately chosen to cover a range of breeds and ages.

The three cocker spaniels, one papillon, a Labrador and a mongrel were taught to focus on an "odour signature" in urine that signaled bladder cancer.

The animals learned to ignore differences in the urine samples caused by sex, age, infection, bleeding or diet.

In the tests, urine from 36 bladder cancer patients and 108 others were used.

Each dog was presented with one urine sample from a person with cancer and six controls without cancer. They identified the cancerous sample by lying next to it.

As a group, the dogs correctly flagged the positive sample 22 times out of 54, for a success rate of 41 per cent.

By chance alone, the expected success rate would be 14 per cent.

"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 British scientists wrote in the Sept. 25 issue of the British Medical Journal.

"The most intriguing finding was the control patient seen during the training phase, whose urine sample was consistently identified by the dogs as a case," wrote T.J. Cole of the Institute of Child Health in London in a BMJ commentary.

The control patient's test results were negative, but the consultant was so impressed by the dogs' performance that the patient was tested again. Kidney cancer was found, said Cole, who owns a chocolate Labrador.

The researchers were inspired to conduct the study after another pair of English doctors reported a pet Labrador started to persistently sniff a patch of eczema on his owner's leg, through his trousers.

The man turned out to have developed skin cancer. Once the tumour was removed, the dog ignored the eczema patch. There have also been similar anecdotal reports.