BioEd Online

Dogs have always taken an inordinate interest in urine. But now UK researchers have put that penchant to good use, and shown that the animals can detect signs of bladder cancer in human pee.

The idea that dogs' super-sensitive noses might sniff out the scent of cancer stems from patients' anecdotal experiences with their pets. One of the first cases to reach the medical literature reported a woman who had gone to the doctor after her dog started sniffing suspiciously around a skin sore. It turned out to be a malignant tumour¹.

To formally test dogs' ability to diagnose disease, dermatologist Carolyn Willis at Amersham Hospital, UK and her team started training six dogs of varying breeds to detect the urine of patients with bladder cancer. Researchers believe that cancer cells release molecules into the urine that have a characteristic smell.

The dogs worked with trainers for seven months. To teach the dogs the unique odour signature of cancer, compared to those of infections, inflammation or blood, their trainers coached them to discriminate between the urine of cancer patients and those with other bladder conditions.

When the trained dogs were put to the test, they were "remarkable", says Willis. They were asked to choose between laboratory dishes of seven types of urine and lie down in front of the one from a cancer patient. The dogs were correct over 40% of the time, way above the 14% figure that would be expected if they chose by chance².

In one instance during the training, the dogs repeatedly chose the urine of a supposedly healthy patient. When doctors did further tests, they discovered a burgeoning kidney cancer.

Disease warning

Other research groups are already testing dogs' ability to sniff out early signs of skin or prostate cancer. By smelling urine, breath or skin, they might also nose out a range of other diseases.

Willis acknowledges that the dogs are not expert enough to start routinely performing diagnoses, which need to be far more accurate. "None of us envisages dogs replacing doctors," she says.

But she hopes to gradually sift through the molecules in patients' urine and use the dogs to help identify which ones are warning signs of bladder cancer. These molecules could then be used to make diagnostic tests for use in the lab.

In some cases, however, the cocktail of aromas that indicates a particular disease may be so complex that dogs are best at detecting it, says James Walker at Florida State University in Tallahassee. Walker says that he and a team have already shown that dogs can sniff out skin cancers by training them on human tissue.