Can Dogs Smell Cancer in a Person?

Many of us have heard anecdotal stories about the ability of dogs to sense when a person is unwell. We may think of this skill as an indication of the strong bond between humans and dogs. Or, simply evidence of the superior scent-detection abilities of canines.

Research has demonstrated that in some instances, dogs do have an inert ability to tell when a person is suffering from an illness, before they even find out themselves. Dogs can also be specially trained to identify markers of specific diseases. In combination, this gives credence to the idea that dogs can smell cancer.

In this article, we’ll explore the ways in which canine behaviour can indicate illness, the history and research behind the phenomenon, and ways that dogs can be trained to detect cancer. 

In dogs that are not specifically trained to detect cancer, their reaction to a possible illness can vary. Many owners have reported a noticeable change in behavior in response to the presence of a person who subsequently discovers that they have cancer. Some dogs will whine, bark, or howl, with no other obvious cause. They may relax when the person has left the room, or they may show signs of distress at their departure.   

Dogs can become clingy and protective of a person who is ill, and show signs of guarding. They may be agitated if the person is approached by someone else, which could present as growling, barking, or dropping their ears. Other dogs will focus on a specific area of the body, which turns out to be indicative of the location of cancer development. In this instance, dogs may nuzzle or paw at the area, consistently sniff it, whine, or howl.

Dogs that are trained to detect cancer in humans, usually from urine, breath, or - in the case of skin cancer - proximity to the affected area, will react with the gesture they have been taught. This could be lying or sitting down next to the afflicted person, nudging them, or giving a vocal indication; although, it is unlikely that barking would be encouraged in this context. Dogs will be trained to indicate as discretely as possible, so as not to alarm a person who may be unwell.

Although there has been subjective evidence of dogs’ ability to detect illness in humans for centuries, it was not until 1989 that the phenomenon was described in a scientific journal. In a 1989 edition of The Lancet, two dermatologists explained a case in which one of their patients was referred - partly due to the reaction of her dog to a mole on her upper leg. The change in her pet’s behavior, and focus on that area, in particular, gave her cause for concern. As it turned out, the mole had developed signs of cancer, and treatment was given.

The patient’s dog had acted as a conduit for early detection, which is a crucial aspect of cancer survival.

Subsequent empirical analysis of the phenomena has shown promising outcomes. One study demonstrated that dogs had a 99% chance of accurately predicting lung cancer from the urine of afflicted patients, although this was not performed on a large scale. 

Similarly, dogs have shown an ability to identify patients suffering from lung cancer based solely on a sample of their breath. Again, this was a small study, and the rate of prediction was slightly lower than the study involving urine detection, but it remains an encouraging area of research. In fact, the British National Health Service has approved further research into canine detection of disease.

Dogs have evolved to possess a highly-sensitive sense of smell - 40 times more powerful than that of humans! This is due to a combination of factors; 300 million receptors in their noses, a specific flow of air to detect scent, and a superior ability to interpret the molecular profile of everything they encounter. 

This ability allows dogs to track, hunt, and detect danger with incredible accuracy. It is also highly beneficial to humans. During a visit to the airport or a busy event, you will often see trained dogs weaving through the crowds with their handlers. The natural ability of canines has been finessed to help us detect narcotics, explosives, and other indications of criminal activity. 

It’s a similar mechanism for cancer detection. Current research points to their ability to identify small amounts of compounds that are produced by malignant tumours, whether in urine, breath, or around the area of disease. 

Although all dogs are excellent sniffers, some have a superior aptitude, as well as a behavioral profile that makes them more receptive to training. These include Beagles, Labradors, and German Shepherds.

Training will generally begin at a young age, in order to maximize a dog’s potential to learn the skills required for accurate prediction. Let’s take detection of cancer from urine as an example. In the first instance, dogs will present with various samples of bodily fluids and other scents. They will be rewarded whenever they make an accurate identification of any urine sample. This behavior is finessed until a dog can competently recognize urine, and disregard other scents.

Dogs will then be trained to identify the compounds present in the urine of patients with cancer. Again, they are presented with several urine samples; some from healthy patients, and some from those with active disease. Dogs are rewarded only when they indicate that a sample contains the correct compounds. Over time, this encourages dogs to become more accurate, to the point that they can competently predict whether a patient has signs of cancer.

Note that research into the ability of dogs to specifically detect the presence of cancer in humans is ongoing. It remains an promising area of investigation, and larger-scale studies will be required; not only to better understand the mechanisms involved, but to determine how man’s best friend can help us identify different types of cancer in the future.