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Early cancer detection is critical for increasing patient survivability; however, current methods for early detection are costly and often inaccurate. It is of great importance to find other, more cost effective and accurate methods for early cancer detection, and to do this, we may need to turn to new and unconventional methods.
It’s often been said that dogs can sense the supernatural, whether people are good or bad, and thunderstorms, long before they occur. With their acute sense of smell, dogs are able to detect minute changes in the air composition around us – an ability humans lack. This difference in the sense of smell is due to the difference in nose design between dogs and humans. Olfactory receptors are the part of the nose that smells smells, and dogs harbor about 40 times more than humans. Therefore, dogs can be 10,000-100,00 times more sensitive to smells than humans 1,2. According to Dr. Alexandra Horowitz, a dog-cognition researcher at Barnard College, this means that while we might notice if we add a teaspoon of sugar to coffee, a dog could detect a teaspoon of sugar in two Olympic-sized pools worth of water.
Just as the air can have certain molecules and change – for example, if you spray some perfume – blood can also change scents when certain molecules are present. Certain cancers emit certain molecules, or smells, that cannot be detected by humans, but can be detected by animals with acute senses of smell, such as dogs! In a recent study, beagles were trained to detect cancer from blood samples. Beagles were chosen for the study due to their impressive sense of smell, along with their trainability and sociable personality. Beagles have 44 times more (220 million versus 5 million) olfactory receptors than humans, and among dogs, they have one of the keenest senses of smell.
To train the beagles for cancer detection, they were allowed to sniff blood samples from patients recently diagnosed with non-small lung cancer but not yet treated – blood containing drugs would smell different than blood without drugs. Once trained, the dogs were presented with different cancer and non-cancer samples. In one day, three beagles performed ten examinations, sniffing different samples. If a dog thought that a sample was cancerous, they were trained to sit in front of that sample. If the dog thought the sample was non-cancerous, the dog ignored it and moved on to investigate other samples. A 10-minute rest period occurred each time the samples were changed out, which allowed the odor from the previous test to dissipate and the scent from the new samples to accumulate in the area. In total, the study included samples from ten patients, including males and females, a range of ages, and different racial background.
Between the three beagles, 93% (28/30) of the samples were correctly identified as cancerous. This suggests that dogs are able to identify cancers through smell! However, this study was small, and does not determine whether dogs could identify cancer at different or earlier stages, it only determined that dogs could identify cancer through smells. The samples the beagles detected had already been marked as cancerous through other detection methods.
This study does bring up many interesting points to consider through future research. If the dogs can identify cancer via smells (which, again, are caused by the presence of certain molecules), can we identify what those molecules are, and then use them as biomarkers in the future to screen for cancer? Can dogs identify whether relapse occurs, and can dogs also determine whether other diseases are present along with cancer, such as diabetes? More studies like this need to be conducted before we can be confident in moving forward with using dogs to detect cancer. However, if future studies see similar results, we may have a powerful new tool for early cancer detection. This new tool would be especially important for underserved rural communities, where the price of medical examinations are often too costly.
- Walker, D. B., Walker, J. C., Cavnar, P. J., Taylor, J. L., Pickel, D. H., Hall, S. B., & Suarez, J. C. (2006). Naturalistic quantification of canine olfactory sensitivity. Applied Animal Behaviour Science, 97(2), 241-254. doi: https://doi.org/10.1016/j.applanim.2005.07.009
- Junqueira, H., Quinn, T. A., Biringer, R., Hussein, M., Smeriglio, C., Barrueto, L., . . . Huang, X. Y. M. (2019). Accuracy of Canine Scent Detection of Non–Small Cell Lung Cancer in Blood Serum. J Am Osteopath Assoc, 119(7), 413-418. doi: 10.7556/jaoa.2019.077