News about disease-detecting dogs has proved irresistible to headline writers, who’ve come up with gems such as “A new PET scan,” “Doggie Howser,” and “You’ve heard of the CAT scan; now here’s the DOG scan.”

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 April 2007 | Back to Table of Contents


The Scent of Sickness

Dog detectives track cancer.

On average, dogs’ noses are estimated to be between 100,000 times and 1 million times more sensitive than a human’s. Breeds considered to be scent hounds are reputed to have a sense of smell 10 million to 100 million times more acute than that of the average person. Dogs have long proved useful to us because of this. Trained dogs have successfully tracked individuals through densely populated areas, found people buried by avalanches or the wreckage of earthquakes and bomb sites, and located bodies submerged in lake water. They might next be able to detect disease, according to several published studies.

In a 1989 letter to the British medical journal The Lancet, a woman in England said she sought medical attention because her dog had been sniffing persistently at a mole on her leg and whining; finally the dog took a nip at that area of her leg. Her doctor subsequently excised the mole, and it proved to be melanoma. Soon, more anecdotal evidence for dogs signaling cancer in their owners came to the fore, and researchers became interested in the possibility that dogs could detect volatile organic compounds present in cancer patients that were previously undetectable by conventional means.

In 2004, the British Medical Journal published a study by Willis, Church, et al. that tested dogs’ ability to identify bladder cancer from urine samples. The researchers trained six dogs of varying ages and breeds to lie or sit when they encountered a sample from a known bladder cancer patient. In the training phase, the control group included people considered “healthy” (among other screening tests, study participants older than 30 were required to undergo cystoscopy to eliminate those with visible bladder malignancy), those with other urologic disorders, individuals with other diseases such as diabetes, and menstruating women (trace blood was present in the samples). Tests were double-blind, the samples were prepared in a building separate from the testing area, randomization software was used to determine placement of samples, gloves were worn during and changed between handling of samples, and all test runs were recorded on videotape.

Results suggested that dogs may indeed be able to detect bladder cancer from urine samples. The trained dogs were successful in signaling cancer correctly 41 percent of the time, as compared with 14 percent expected by chance alone. Some dog experts have noted that results might have been better if “scent breeds” had been used.

A recent study published in the May 2006 issue of Integrative Cancer Therapies tested dogs’ ability to detect lung and breast cancer from breath samples. After a training period of two to three weeks with samples from known cancer patients, five dogs (three Labrador retrievers and two Portuguese water dogs obtained from Guide Dogs for the Blind) were tested on exhaled breath samples from 86 cancer patients and 83 healthy people. The lung cancer patients included both smokers and nonsmokers.

The dogs detected lung cancer with overall accuracy of 99 percent when adjusted for the confounding factor of the patient being a smoker; for breast cancer, the dogs were 88 percent accurate. The authors note that their results may overestimate the dogs’ accuracy because participants in the control group were all healthy. Results might have been different had they included people with other inflammatory diseases such as mastitis or fibrocystic breast disease in the breast cancer test group, or emphysema or bronchitis in the lung cancer control group.

Human interest value notwithstanding, clinical implications of these studies will not be dismissed easily; the researchers who published their study in the BMJ stated that their “intention, at this early stage, was not to investigate the clinical usefulness of dogs’ capabilities but to conduct a simple ‘proof of principle’ experiment” with the hope that future investigations might aid in the development of “artificial sniffers” that will identify volatile organic compounds specific to cancer patients. The refinement of gas chromatograph/mass spectroscopy technology is often mentioned as the next step toward the practical application of the findings from the experiments with dogs.

At least one person is convinced of the efficacy of dogs’ cancer-detecting ability: During the training phase of the bladder cancer study, all six dogs consistently signaled “cancer” for a urine sample that came from an individual screened before the study as “healthy.” On further investigation, the person was found to have a transitional renal cell carcinoma.—Connie Martin


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