Are Canine Cancer Sniffers the Real Deal?

Lung cancer is a common cancer in Europe. A 2012 study reported that it was the third most common cancer (410,000 cases) and the most common cause of death from cancer (353,000 deaths) in Europe, highlighting the need for early and accurate diagnostic lung cancer testing.

Previous studies have used gas chromatography-mass spectrometry to identify several volatile organic compounds (VOCs; i.e., 1-butanol and 2-pentanone) as potential lung cancer biomarkers; these VOCs were found in greater concentrations in the breath of patients with lung cancer than in that of healthy patients. Interestingly, several studies have described dogs’ olfactory ability to detect these potential biomarkers. However, the reported sensitivities and specificities for this detection ability varied widely.

To date, few studies have investigated dogs’ cancer-detecting abilities alongside instrumental VOC analysis. In addition, no single VOC or combination of VOCs has reached clinically relevant specificity and sensitivity for disease recognition. In a proof of concept study recently published in Frontiers in Veterinary Science, a German research team determined that dogs could be a valuable tool for lung cancer diagnosis.

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Sample Collection and Training

The researchers obtained “genuine” breath samples from 30 patients with lung cancer who had not yet begun treatment and 30 healthy patients. They also prepared 4 synthetic air samples containing several VOCs: 1-butanol, 2-butanone, 2-pentanone, and hexanal. All samples were placed in fleece-lined sample tubes that were then placed within cones. These breath samples were used for training and testing.

Four female pet dogs of various breeds were trained to distinguish between breath samples from patients with lung cancer and healthy patients; sniffing of the cancer-positive samples was immediately rewarded with a treat. Only 2 of the dogs—a Labrador and poodle—successfully completed training and were used for testing.

Testing and Results

The dogs first underwent several trials to distinguish between breath samples from patients with lung cancer (n=9) and healthy patients (n=10). In the testing room for each trial, several sample-containing cones were positioned in front of the dog. The dog’s initial contact with each sample was analyzed: sitting near a sample or pointing the nose at it indicated positive (lung cancer) and walking away from a sample indicated negative (healthy). Dogs had to indicate positive or negative for all samples, and correct positive indications were rewarded with a food treat.

Of the 9 samples from patients with lung cancer, the Labrador correctly identified all 9 and the poodle identified 8 as positive. Of 10 samples from healthy patients, the Labrador correctly identified 8 and the poodle identified 4 as negative.

Next, the dogs distinguished between the synthetic air samples (n=4) and samples from healthy patients (n=10). Each dog correctly identified 3 synthetic air samples as positive.

Bringing It Together

The researchers acknowledged several study limitations, particularly the low number of dogs used for testing. However, they noted, the results still provide proof of concept. Because of this, the researchers believe that “specially trained detection dogs are a useful tool for finding the best possible biomarker for an effective diagnostic system for lung cancer.”

For future research on using dogs for detecting human cancer, the researchers suggested determining specific selection criteria for detection dogs and evaluating more combinations of VOCs that could be lung cancer biomarkers.

Dr. Pendergrass received her Doctor of Veterinary Medicine degree from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, a medical communications company.