Is it true that animals can smell cancerous growths?

Endal the incredible dogThe idea that animals can sniff out an illness that has been around for a long time. When it comes to finding cancer, however, scientists certainly don’t turn their noses up at the prospect. It is known that cancerous cells produce their own particular set of chemicals and it is also well known that many animals are particularly sensitive to small changes in airborne substances (dogs’ noses in particular). Anecdotally, there are many stories of dogs and other pets seemingly indicating the presence of a cancer in their owners. But what does the actual evidence say?

Well, so far the published research is conflicted; some studies show that animals may be able to sense cancer while others disagree. Potentially the most positive study so far examined whether a specially-trained Labrador could detect colorectal cancer (bowel cancer) from breath and stool samples (it sounds horrible, I know). The study’s results suggested that the dog’s accuracy was up to an incredible 99%! Other studies, however, have not seen such a remarkable result.

One experiment, for example, that used double-blind tests (a good way of making sure the researchers don’t accidently affect the results) showed that specially trained dogs were no better than random chance at detecting prostate cancer. While a separate study testing dogs’ ability to detect lung cancer detection was a mixed bag of treats: the dogs recognised 80% of the people who had cancer but also poked their noses at a large number of people who did not have cancer, meaning that any benefit was lost due to the very high number of false readings. Overall, the research seems to suggest some animals may be Lassie-like in their ability to recognise cancer but that the technique is not reliable enough for medical purposes.

What about other diseases? Many diseases have distinctive smells. One in particular is Type I diabetes. When a Type I diabetic has low blood sugar, their body creates substances called ketones which can leave the body in the breath. One commercial outfit (Dogs4Diabetics) claims to sell trained dogs that can smell ketones and ‘tell’ the owner when their blood sugar levels are dropping dangerously low – potentially before they would otherwise realise.

Using animals to help diagnose people is an interesting idea and dogs seem to be the top companion for the medic. Who knows, perhaps in the future we might hear from the waiting room: “Mrs Smith, the dogtor will sniff you now”?

Answer by James Crewdson

Photo caption: Endal wearing his PDSA Gold Medal. During a 2001 emergency saved a man, Endal retrieved his mobile phone from beneath the car, fetched a blanket and covered him, and then ran to a nearby hotel to obtain help.

Article by James Crewdson

June 4, 2015

James Crewdson is a Clinical Medicine student at Imperial College London, having already completed a BA in Biological and Biomedical Science at Gonville and Caius College, University of Cambridge. He has a keen interest in all of biological sciences and in the happenings of Manchester City Football Club, the best team in the land and all the world. You can get in touch with him on Twitter at @JamesCrewdson1.


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