Can Dogs Smell Cancer? Exploring Cancer-Sniffing Canines

When it comes to their sense of smell, a dog’s sniffing ability operates on a whole other level compared to ours. They can sniff out hidden treats, and there are even trained bed-bug sniffing dogs! But could a dog’s nose be so good that it could sniff out cancerous cells? 

Yes, some dogs do have special cancer-sniffing abilities — but usually it’s only if they’ve been trained. However, there are some cases of average dogs who have shown cancer detection abilities without being trained.  

Can Dogs Sense Cancer?

The first published evidence of a cancer-sniffing dog appeared in 1989 in the medical journal Lancet. Two physicians wrote a letter about a dog who became obsessed with a mole on his person’s leg. The mixed-breed dog constantly sniffed at the mole and eventually tried to bite it off. Although his owner wasn’t particularly concerned about the mole, her dog’s persistence convinced her to have it checked out. The mole was indeed a malignant melanoma (skin cancer). 

Since that time, dogs in special training programs have been able to detect cancer in human tissue, blood, urine and breath samples, enabling them to identify skin, bladder, prostate, colorectal, breast and lung cancers, in addition to ovarian cancer. 

The trained dogs can’t differentiate breast cancer from prostate cancer (or any other type of cancer), but the dogs can detect the scent of volatile organic compounds given off by the malignant (cancerous) cells in the human body. Only a doctor can diagnose a disease, but these highly trained cancer-detection dogs are able to contribute to valuable cancer research studies.

Can Untrained Dogs Smell Cancer?

There’s typically no need to tense up every time your dog runs their snout over your skin; dogs that can detect cancer generally only do so after intensive training. If your dog is licking your skin or focusing on a particular part of your body, it’s more likely that you spilled some food or there’s another substance there that smells or tastes interesting to your dog. However, there are rare, personal accounts of untrained dogs’ behaviors that convinced their owners to consult their doctor and confirm a diagnosis.

Can Dogs Detect Cancer by Licking?

No, dogs that have been trained to detect cancer do so by sniffing not licking. Dogs have around fifty times as many scent receptors as humans, or about 300,000 of them. And unlike people, dogs have a second scent organ located on the bottom of the nasal passage called the vomeronasal or Jacobson’s organ, to aid in detecting even more scents. This powerful olfactory system enables them to detect scents like the volatile organic compounds given off by the cancer cells. 

However, in anecdotal stories of dogs alerting their owners to signs of potential cancers or tumors, they may have done so by licking, sniffing or nipping at a certain spot on their owner’s body.

How Do Dogs Act When They Smell Cancer?

In untrained dogs, there have been reports of dogs persistently licking, sniffing or nipping at cancerous skin lesions. Others have reported the dog sniffing or pawing at the area where the cancer was later found. 

In trained cancer detection dogs, how the dog acts depends on what they’ve been trained to detect. In general, trainers start by exposing the dog to blood samples or tissue samples from cancer patients. If the dog can alert to the correct sample, they are rewarded with praise and a treat or toy. Through positive reinforcement, the dog is rewarded each time they differentiate the cancer sample odors from other scents.

Can Dogs Tell When You’re Sick?

Your dog knows what you usually smell like, and when you’re sick your smell changes due to changes in your body chemistry and hormones. Some dogs may pick up on this change in smell and realize that something isn’t right. They may also notice that your routine has changed, and now you’re lying on the couch or in bed all day instead of going to work. Some dogs can also read human emotions and may notice that you’re not your usually happy self. 

If your dog comes over to comfort you when you’re sick, there can be a couple of different reasons for this. They may be trying to make you feel better, or they may feel worried about the change in your behavior and routine and need comforting themselves. Your instinct is, of course, to snuggle with your canine companion, and this positive reinforcement means that the next time you’re sick, they’ll want to snuggle with you again. But a little snuggle therapy is good for everyone.

What Is the Future for Cancer Medical Detection Dogs?

Currently, dogs are only trained to detect cancer in medical samples, not in people. These canine scent detection training centers collaborate with other cancer research scientists who are working to isolate the exact chemicals the dogs identify. Since the accuracy of the dogs can vary depending on a number of factors, including breed, level of training and handler bias, the hope is to eventually create an electronic sensor that can essentially replace the dogs.

But for now, these trained dogs are applying their noses to help researchers get one step closer to early detection of many human cancers. Amazing, isn’t it?