The realm of colorectal cancer screening recently has expanded in an unlikely direction; namely, the sense of smell. Researchers at Kyushu University in Fukuoka, Japan recently have shown that a dog can accurately detect CRC based on patient breath and stool samples. Their results, which are published in Gut, the medical journal affiliated with the British Society of Gastroenterology, showed a sensitivity of 0.91 and 0.97 for breath and watery stool samples, respectively. The potential to detect CRC by scent offers the promise of treating this relatively common cancer earlier, and hopefully with a better outcome.
The study centers around a single, extensively trained 8-year-old black Labrador Retriever. The dog's ability to detect CRC was tested during a series of trials which spanned several months and more than 250 patient samples. In each trial, four samples were controls, while one sample was positive for CRC. New patient samples were provided for each trial. When the dog discovered a CRC sample, it was trained to sit in front of the sample.
In an effort to standardize samples, the researchers matched the background characteristics of the cases and controls with a range of variables that included age, gender, smoking status, anticoagulant therapy and gastrointestinal complaints - such as constipation, diarrhea, history of colorectal disease or bloody stool.
This last characteristic is of particular importance because it is the basis for the routine CRC screening tool, fecal occult blood testing. This low-budget screening is often the first test to detect CRC, and if positive, is often followed by either a flexible sigmoidoscopy or a traditional colonoscopy.\nFor this study, researchers were keen to point out that the dog's scent judgment did not hinge on the presence - or absence - of blood in a patient's stool sample to determine whether it was a case or control, thereby eliminating the potential argument that the dog's detection would simply reconfirm FOBT.
Although the study results look promising, there remain several challenges to transforming its findings into a screening tool for CRC. First, studies previously have shown that handlers can influence the performance of dogs in "detection" exercises. But there is no mention of ways in which researchers specifically controlled for this potential bias. Second, to strengthen the argument that a "cancerous" odor is indeed detectable, researchers would need to show reproducible results either by other dogs or other animals. Otherwise, it could be argued that these results are simply the work of a particular dog.
And lastly, the real crux to applying the results of this study into a CRC screening protocol lies in identifying the composition of the cancerous odor this dog has been able to recognize. Until this composition is discovered, the ability to use scent as a tool for detecting CRC is limited. Still, the potential to use scent for the detection of CRC, as well as other cancers, is an exciting new forefront in cancer research which may be realized in the coming years.
Andrew Matz is a University Medical student. He can be reached at aam6t@virginia.edu.
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