Reports of dogs sniffing out cancer in humans offer hope that animals could warn of the disease in its early stages. However, new results published in Journal of Breath Research indicate that canine scent detection might not be as powerful as expected when dogs are deployed in a real screening situation.
To provide samples for the dogs to test, researchers in Austria and Germany recruited 122 volunteer patients: 29 of the subjects had been diagnosed with lung-cancer, but were not yet treated, and the remaining 93 subjects had no signs or symptoms of the disease.
The project brings together experts from Krems University Hospital, Otto Wagner Hospital, Hochegg State Hospital, Hannover Medical School and the Fraunhofer Institute for Toxicology and Experimental Medicine.
In the screening programme designed by the group, breath samples—obtained from the volunteers—were presented to six highly-trained sniffer dogs in a double-blind manner to eliminate any subjective bias from the trial. The dogs detected 78.6 % of the positives correctly, but only 34.4 % of the negatives.
“Our dogs made mistakes with both positive and negative samples, and I think that one important reason for the inferior results might be that a true double blind situation puts a lot of stress on the animals and their handlers,” commented Klaus Hackner from Krems University Hospital in Austria, one of the institutions taking part in the study. “Success and regular rewards are important for every kind of sniffer detection work.”
The dog squadron consisted of a Golden Retriever, Labrador, Giant Schnauzer, Large Munsterlander, Havanese and German Shepherd. All of the animals had experience in finding buried people or as avalanche dogs in the Austrian mountains and were considered capable of learning a new scent for detection.
To prepare them for the study, the dogs were trained for six months in advance with a total of 150 training samples. These vials consisted of lung-cancer breath samples and healthy controls based on the same inclusion criteria as the test samples.
Hackner believes that there is scope to improve on the results with the right protocol: one that provides the dogs with more regular rewards to keep them motivated and in good spirits.
“This disparity is not likely to be a detection issue; dogs have been shown to have extremely sensitive noses as proven by their use in tracking, bomb detection, and search and rescue, he explains. “However, in contrast to analytical instruments, dogs are subject to boredom, limited attention span, fatigue, hunger, and external distraction.”
Even with modifications to the protocol, questions remain on whether dogs are a practical solution to providing early warning of major diseases. Ideally, cancer screening should be quick, easy and affordable. For these reasons, the pursuit of an electronic device for sniffing out cancer—a so-called ‘e-nose’—remains high on the agenda.