Early detection is paramount in the successful treatment of cancer. Colonoscopies and Pap smears have long been known to considerably lower mortality rates. However, improved screening methods are always needed. For example, lung cancer has a survival rate of about 15% because it is too often detected in the latter stages, which limits treatment options. Currently, imaging and sampling of blood, fluid, and tissue are the staples of diagnosis, but the future may also include a furrier option.
Cancers release volatile organic compounds (VOCs), and those VOCs have distinct odors. Research has found that dogs are well equipped to detect specific VOCs. Canines have long been used to detect drugs, bombs, and cadavers because they have approximately 220 million olfactory receptors, whereas humans have only about 5 million, which translates into a dog’s sense of smell being about 1000 times more acute than a human’s. As a result, researchers are looking into exploiting this talent. One of the first reports of this phenomenon was published in The Lancet in 1989. A case was described where a patient complained about her dog constantly sniffing a mole on her leg, even attempting to bite off the lesion on one occasion. Later, the mole was determined to be a malignant melanoma. A separate report from 2000 describes a man who had a patchy area of eczema on his leg for 18 years. He was prescribed topical steroids and antifungals but the condition never resolved. After the man brought home a new pet Labrador, the dog began sniffing and resting his nose on that portion of patchy skin, even repeating the behavior when the man was wearing pants. The dog’s action prompted the owner to have the affected skin excised, and the laboratory determined it to be cancerous. In both instances, once the cancer was removed, the dogs ceased their strange behavior.
Research into the viability of canine cancer screenings is underway, and current data support it as a viable option. A 2004 study examined whether canines could be trained to detect VOCs in urine samples of patients with bladder cancer. Trained dogs correctly identified positive samples 41% of the time, compared with a 14% random chance. Furthermore, dogs trained to identify VOCs using wet samples outperformed canines trained with dry samples (P=0.03). Although this study had a small sample, it did show potential.
Another study published in 2011 examined canine scent detection as it relates to colorectal cancer (CRC). Breath samples were collected from 33 patients with CRC and 132 healthy controls. Watery stool samples were also obtained (37 and 148, respectfully). Accuracy was measured against the results of a traditional colonoscopy. Results showed that there was a high level of sensitivity and specificity: trained canines correctly indicated patients with CRC 91% of the time and healthy controls in 99% of the cases. The stool sample results demonstrated a similar level of agreement, with 97% accuracy for CRC samples and 99% for healthy controls. A study published in the European Respiratory Journal reveals comparable results. The authors attempted to determine the effectiveness of canine screenings for lung cancer. They also used breath samples: 60 from lung cancer patients and 110 from healthy controls. Interestingly, results were relatively consistent with the study mentioned above. The European study demonstrated that dogs showed an overall accuracy of 90% for patients with cancer and 72% for controls.
It has long been known that diseases have particular scents. Hippocrates described a change in the odor of febrile patients in his medical text, the Hippocratic Corpus, Prorrhetics II. Chinese documents from the 3rd century BCE also associate different smells and colors with disease: “Every disease of the five solid organs is reflected in (externally observable) color and smell. For diseases of the liver, it is a greenish color and rank odor.”
Current research is in its infancy and more conformational studies on larger populations must be performed. In the end, canine screenings will most likely only act as a supplement to current screening methods. However, there are still many interesting aspects to this area of study. One researcher is attempting to create a device that detects VOCs in human breath, but the sensitivity of a dog’s nose may not be re-creatable. Until a device is manufactured that can detect VOCs with the sensitivity of a canine’s nose, it looks like detecting cancer may just be for the dogs.
- Church J, Williams H. Another sniffer dog for the clinic? Lancet. 2001;358(9285):930.
- Correa JE. The dog’s sense of smell. ACES. Alabama Cooperative Extension System Web site. June 2011. http://www.aces.edu/pubs/docs/U/UNP-0066/.
- McCulloch M, Turner K, Broffman M. Lung cancer detection by canine scent: will there be a lab in the lab? Eur Respir J. 2012;39(3):511-512.
- McNeil DG. Dogs excel on smell test to find cancer. New York Times. January 17, 2006.http://www.nytimes.com/2006/01/17/health/17dog.html?incamp=article_popular_4&pagewanted=print.
- Sonoda H, Kohnoe S, Yamazato T, et al. Colorectal cancer screening with odour material by canine scent detection. Gut. 2011;60(6):814-819.
- Willis C, Church S, Guest CM, et al. Olfactory detection of human bladder cancer by dogs: proof of principle study. BMJ. 2004;329(7468):712.