Sept. 23, 2004 -- All that time dogs spend sniffing things may have honed their skills as medical detectives. A new British study shows that dogs' exceptional sense of smell may allow them to detect bladder cancer by merely smelling a person's urine.
Researchers say that tumors are thought to produce unstable compounds, which are present in urine and may give off unique scents that are undetectable by humans but may be detected by the average dog.
In their study, a variety of dogs were able to tell the difference between urine from a healthy person or one with bladder cancer with a 41% accuracy rate, which is nearly three times the success rate that would have been expected by chance alone.
"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," write researcher Carolyn Willis of Amersham Hospital in Amersham, U.K., and colleagues. "On balance, the results are unambiguous. Dogs can be trained to recognize and flag an unusual smell in the urine of bladder cancer patients."
Researchers say the study also gives weight to anecdotal reports by dog owners that canines may be able to detect subtle differences in scent caused by cancer.
Fido Finds Cancer
In the study, researchers trained six dogs to discriminate between urine from people with bladder cancer and urine from people with other diseases or healthy individuals. The dogs included a variety of breeds (included three Cocker Spaniels, a Labrador, Papillon, and a mutt) and ages; they had no particular skills in scent discrimination.
After training, each dog was presented with a set of seven urine samples, one from a bladder cancer patient placed alongside six other specimens, which where from people without cancer. The dogs identified the sample they considered to be different by lying next to it. This process was repeated eight times.
Researchers found the dogs correctly identified the urine sample of the bladder cancer patients 22 out of 54 times.
Interestingly, researchers found the tiny Papillon performed almost as well as the Cocker Spaniels, which are known for their hunting skills. The mutt performed the worst.
In an editorial that accompanies the study in the BMJ, Tim Cole, professor of medical statistics at the Institute of Child Health in London, says dogs are widely recognized for smelling things that humans miss.
"Yet the idea of turning this canine skill to clinical diagnosis is novel," writes Cole.
But Cole says the most intriguing finding of the study was the nonbladder cancer patient who was used as a control during the training phase, whose urine sample was consistently identified by the dogs as different.
Despite the fact that the individual had been tested for cancer, the doctor responsible for the patient was sufficiently impressed by the dogs' performance to test the patient again and found a tumor in the kidney.