In the treatment of cancer, early detection is often a patient’s best hope for success. Screenings such as colonoscopies and Pap smears have lowered mortality rates considerably. However, improved screening methods are still needed. Presently, lung cancer has one of the highest associated mortality rates. Too often it is detected in the latter stages, which limits treatment options. Lung cancer has an overall survival rate of about 15%. Imaging and blood, fluid, and tissue samples have been diagnostic staples, but the future may also include a different kind of PET scan.
Newer screening methods are being explored based on the concept that cancers release volatile organic compounds (VOCs) and that those VOCs have distinct odors. Oddly, research suggests that canines may be the best equipped to detect VOCs. For years canines have been used to detect bombs, cadavers, and drugs. Canines have about 220 million olfactory receptors while humans have only about 5 million. What does this mean? A dog’s sense of smell is about 1000 times more acute than a human’s. For this reason, science has another job for their super sniffers. One of the first accounts of this phenomenon was published in The Lancet in 1989. A patient complained about her dog constantly sniffing a mole on her leg. On one occasion, her dog tried to bite the lesion off. Later, it was discovered to be a malignant melanoma. In a separate report from 2000, it describes a man who had a patchy eczema on his leg for 18 years. He was given topical steroids and antifungals but it never went away. Sometime later the man brought home a pet Labrador. Within a couple of years, his dog began sniffing and putting his nose on that portion of patchy skin. The dog repeated the behavior even when the man was wearing pants. The dog’s action prompted the owner to get the affected skin removed, and it was determined to be cancerous. Furthermore, in both instances, once the cancer was removed, the dogs ceased their strange behavior.
Research into the feasibility of canine cancer screenings is underway and, as absurd as it may sound, current data support it as a viable possibility. In 2004, one study examined if canines could be trained to detect VOCs in urine samples from patients with bladder cancer. Trained canines correctly identified samples 41% of the time, compared to a 14% random chance. Furthermore, canines trained to identify VOCs using wet samples outperformed canines trained with dry samples (P=0.03). Although this study was small, it did show promise.
In a paper published in 2011, researchers examined canine scent detection for colorectal cancer. Breath samples were collected from 33 patients with colorectal cancer (CRC), and 132 samples were collected from healthy controls. They also collected watery stool samples (37 and 148, respectfully). Accuracy was measured against a traditional colonoscopy. Results from the group indicate a high level of sensitivity and specificity. Trained canines correctly chose patients with CRC 91% of the time and healthy controls 99% of the time. The results from the stool samples demonstrated a similar level of agreement, with 97% accuracy for CRC samples and 99% for healthy controls. A report in the European Respiratory Journal details similar results. The authors looked to determine the effectiveness of canine screenings for lung cancer. Again, they used breath samples: 60 from lung cancer patients and 110 from healthy controls. There is a surprising consistency with regard to the results of both studies. The European study demonstrated that canine detection had an overall accuracy of 90% for cancer patients and 72% in choosing the correct controls.
A diseases having a particular scent is not a novel concept. In fact, Hippocrates describes a change in odor of febrile patients in his medical text, the Hippocratic Corpus, Prorrhetics II. Chinese medical texts from the 3rd century BCE 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.”
The current research is in its infancy and more conformational studies on larger populations have to be done. Canine screenings will probably only supplement current screening methods. However, this area of research is fertile. One researcher is feverishly trying to create a machine that detects VOCs in human breath, but the sensitivity of a canine’s nose may not be re-creatable. One day, canines may be as common in laboratories as microscopes or centrifuges. Until some other device can detect VOCs with the sensitivity of a canine’s nose, it looks like detecting cancer is for the dogs.
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