Dogs can be taught to detect human bladder cancer through smell analysis of urine samples, according to results of a proof-of-principle study published in the September 25th issue of the British Medical Journal.

Tumors are thought to produce volatile organic compounds with distinctive odors. Even when present in minute quantities, it is possible that they can be detected by dogs, with their exceptional sense of smell.

The study involved urine samples from 36 patients with bladder cancer and 108 control samples from diseased (but non-cancerous) and healthy individuals; 63 of the samples were used exclusively in final testing of the dogs.

Six dogs of varying breeds and ages were trained over seven months to discriminate between urine from patients with bladder cancer and that from control individuals.

For the final tests, each dog was offered a set of seven urine samples, comprising one bladder cancer sample and six sex-matched controls. Some controls were also age-matched and most had some form of non-malignant urological disorder. The dogs identified their chosen sample by lying next to it. Each dog performed a total of 9 separate tests.

Taken together as a group, the dogs correctly selected bladder cancer urine on 22 out of 54 occasions, an average success rate of 41% compared with 14% expected by random chance. The dogs' capacity to recognize a characteristic bladder cancer odor was independent of other chemical aspects of the urine such as the presence of blood.

"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," wrote the authors. "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."

"The study was carefully designed to include several features to minimize bias, and it is hard to fault the study in this respect," wrote an expert in medical statistics in an accompanying commentary. "On balance the results are unambiguous. Dogs can be trained to recognize and flag an unusual smell in the urine of bladder cancer patients."