#79 Can dogs smell cancer?

I learned this today. Dogs can probably smell cancer in people.

Dogs have a phenomenal sense of smell. They have 300 million olfactory receptors in their noses. We have about 6 million. On top of this, the part of their brain that is devoted to analyzing smells is about 40 times larger than ours. It has been estimated that dogs can smell 10,000 to a million times better than we can, depending on the type of dog. We have a larger area of our brain devoted to sight, which is why we can see better than a dog can.

Smell works because of sensory cells, called olfactory sensory neurons, inside the nose. These cells are connected directly to the brain. There is one odor receptor in each olfactory neuron. When molecules released by substances evaporate, they can float into our noses and stimulate these receptors. The receptor sends an electrical signal to the olfactory bulb in the brain, which analyzes the chemical composition of the smell. The smell is deciphered and compared to other known odors. This part of the brain is also connected to the hippocampus and amygdala, the parts concerned with emotion and memory. That is why smells can evoke memories or feelings.

The sense of smell is so advanced in dogs, that they can detect a single drop of liquid in 20 Olympic-size swimming pools. One part per trillion. The structure of a dog’s nose is also different from ours. When we breathe in, the molecules enter our nose, but when we breathe out, we expel them with the exhaled air. Dogs breathe in and out through different parts of their nose. They breathe in through the nostrils at the front, bringing molecules onto their olfactory sensory neurons. When they inhale, a fold of tissue separates their nose and the breath they exhale is forced out through slits at the side of their nose. This means the odors are not expelled and they can smell continuously.

They can also angle their nostrils far more than we can, allowing them to detect the direction a smell has come from. And they are able to analyze the intensity of a smell and judge how long ago the smell was created. They can smell emotions, such as fear and anxiety. They can smell adrenaline and they can smell the chemicals released by increased heart rate and blood flow.

So, how does this connect to cancer? It turns out that dogs can probably smell cancer. I say “probably” because the research is still ongoing. However, what research has been done seems to indicate that dogs are able to detect cancer by sniffing skin, breath, urine, feces, or sweat. They are correct more often than they would be by chance.

What are they smelling? Again, there is not a definitive answer yet, but they could be smelling polyamines. Polyamines are molecules that play an important role in cell growth, proliferation, and differentiation. They bind to DNA. Cancer is caused by increased cell proliferation, which will raise polyamine levels. Polyamines smell bad. At very high concentrations, humans can smell them, but at the concentration from cancerous cells, we cannot. Researchers have tried to make electronic noses that can detect these polyamines. That is possible, but they are expensive. Then, someone realized that dogs can smell polyamines.

There were stories of dogs sniffing their owners and then pawing at moles or pawing at someone’s stomach. When these people got checked, it turned out that they had cancer. This led scientists to think that maybe the dogs were able to smell the polyamines.

Dogs can be trained to sniff for certain scents. There are drug dogs, cadaver dogs, bomb dogs, tracking dogs, and each dog is trained to respond when it detects a certain scent. It seems that dogs can be trained to sniff for polyamines and react when they detect them. So far, trained dogs given a selection of urine samples pretty much always pick the one from the person with cancer. If this turns out to be 100% foolproof, then there is a simple and cheap way of detecting cancer. All because dogs have insanely powerful noses.

Interestingly, yet unconnected to this, the African elephant has the strongest sense of smell of any animal. Probably twice as good as a dog and they can smell water up to 19.2km away.

So, dogs have an incredibly strong sense of smell, and it appears that they are able to smell polyamines which are produced when cancer cells proliferate. If this turns out to be true, then we could see medical sniffer dogs in the future. And this is what I learned today.

Photo by Simon Robben from Pexels

Sources

https://www.nidcd.nih.gov/health/smell-disorders