We’ve known for some time that dogs can be trained to detect some types of human cancer. In a new study, researchers have shown that our best friends are also able to smell bladder cancer in other dogs’ urine.

If we want to fight cancer, detecting it early is essential. However, cancer symptoms can be vague, and investigations are time-consuming and sometimes invasive. In the veterinary world, it’s not much different. In fact, it’s much harder. The patient can’t explain to the doctor how they feel and identifying symptoms can be even more challenging. Cancer tests for dogs are often costly, stressful, and invasive.

This is exactly where the new study comes in.

We already know that dogs have an amazing sense of smell. They’re employed to detect bombs, drugs, or even certain diseases like diabetes and epilepsy. Previous studies have shown they can detect some types of cancer (like prostate and lung cancer) in humans — so why not also in dogs?

The scent of cancer

That’s the idea behind the new study from Isabelle Desmas-Bazelle and colleagues. Three dogs participated in the trial: two cocker spaniels and a Labrador retriever. All three dogs were previously trained to detect human cancers. The dogs underwent an additional 29 days of specialized training, learning to distinguish between urine samples from dogs with ulcerative colitis (UC) and those from healthy controls or dogs with non-malignant urinary diseases.

Samples were rigorously selected and coded to prevent bias. Importantly, the study used leftover urine from routine diagnostic procedures, ensuring that no dogs were subjected to additional discomfort.

In a double-blind trial, each detection dog was presented with a mix of UC-positive and control urine samples. The results were striking:

• Sensitivity — the ability to correctly identify positive samples — averaged 80%.
• Specificity — the ability to ignore control samples — was 91.7%.

This is comparable to specialized diagnosis tools.

Why this matters so much

Around one in four dogs will develop cancer during their lifetime. Dogs develop cancer at a similar rate to humans, and bladder cancer is one of the most common types of cancer in dogs. However, the disease can resemble other urinary tract disorders (or bladder stones), which makes it more difficult to diagnose.

This isn’t the first attempt to train dogs to detect this type of cancer. A prior study had disappointing results, with dogs failing to distinguish cancerous urine from healthy samples. Researchers attributed the failure to factors like a small sample size and insufficiently varied training samples, which may have led the dogs to memorize specific donors rather than detect cancer itself.

Using urine is also important. Urine provides a practical advantage for researchers and clinicians. Large volumes can be collected and stored for analysis, making it an ideal medium for ongoing studies and training detection dogs.

For bladder cancers like UC, urine is the most logical medium because it directly contacts the tumor. Moreover, collecting urine is relatively straightforward and stress-free for most dogs. Free-catch urine samples — where dogs simply urinate into a sterile container — are far less invasive than collecting saliva or drawing blood, especially for dogs that are fearful or uncooperative in clinical settings.

Applying this in the real world

The idea is exciting, but bringing it into the real world will be challenging. To truly kick-start doggie diagnosis, researchers suggest the following steps:

• Training more dogs: With proper training programs and facilities, more dogs could be trained to detect other types of canine cancers as well.
• Screening Breeds at Risk: Some breeds, like West Highland White Terriers and Scottish Terriers, are more prone to UC. Detection dogs could screen these high-risk breeds regularly, catching cancer early when it’s more treatable.
• Complementing Existing Tests: Detection dogs could serve as a first-line screening tool, with positive results confirmed by traditional methods like the BRAF mutation test or imaging.
• Non-Invasive Diagnostics for Anxious Dogs: For pets that can’t tolerate invasive procedures, a simple urine test with a detection dog could provide a much-needed alternative.

Furthermore, the sample size in this study was relatively small, and more research is needed to see how detection dogs perform in larger, more diverse populations. Additionally, factors like diet, medications, and environmental exposures could affect urine scent profiles, and researchers need to understand how these variables influence detection accuracy.

There’s also the challenge of practicality. Maintaining a fleet of trained detection dogs requires time, resources, and skilled trainers. However, as technology advances, the insights gained from these canine superheroes could inform the development of “electronic noses” — machines designed to mimic canine olfaction for widespread clinical use.

But with continued research and investment, these four-legged diagnosticians could transform veterinary medicine, offering early detection, hope, and more wagging tails in the process.

The study was published inVeterinary Oncology.