Cancer and Genes in Dogs: What Breed, Genetics, and DNA Can (and Can't) Tell You

The word "cancer" always stirs worry in a dog parent's heart. In the past, when we talked about cancer in dogs we tended to focus almost entirely on "breed" and "genes passed down from the parents." But today, research from around the world is inviting us to rethink the relationship between genes and canine cancer. Today I, Dr. Mon, would like to walk you through what we actually know, so we can understand it correctly and face it with more hope.

In 1 Minute

• Roughly 1 in 3 dogs may develop cancer in their lifetime, and the risk varies widely between breeds.
• Risk often scales with body size, because larger breeds have more cells that divide more over a lifetime.
• The mutations that drive cancer are mostly somatic, arising later in life rather than being inherited from the parents.
• Mutation patterns depend more on the "type of cancer" than on the "breed."
• Canine cancer closely resembles human cancer, making dogs a valuable model that advances treatment for both.
• A DNA test can indicate a tendency toward risk, but it is not a diagnosis and not a verdict that your dog will get cancer.

Cancer Rates and the Truth About Body Size

Dogs are an extraordinarily diverse species, and sadly they carry a surprisingly high cancer rate. Statistics suggest that about 1 in 3 dogs may develop cancer during their lifetime, and this risk differs markedly from breed to breed, from around 10% in small breeds like the Shih Tzu to over 55% in the Irish Water Spaniel (Institute of Canine Biology).

Research also indicates that cancer risk tends to scale with body size. Larger breeds have more cells and undergo more cell division over their lifetime than smaller dogs. That means the bigger the body and the more cells divide, the higher the natural chance of an "error" at the cellular level. That said, these figures describe populations as a whole, not whether any one individual dog will or won't develop cancer. Read more in Large Breed vs Small Breed.

Most Mutations Aren't Inherited (Somatic vs. Germline)

This is the point that makes us rethink things. Many people assume that if a dog gets cancer, it must have inherited "bad genes" from its parents (a germline mutation). But large studies, one analyzing more than 2,119 canine cancer cases and another of 684 dogs across more than 35 breeds, found something striking: the genetic changes that drive cancer are mostly somatic mutations.

• What is a somatic mutation? It is a mutation that arises after conception, not inherited from the parents. It is a random error that occurs spontaneously during cell division, or is triggered by external factors and cellular stress.
• Mutations depend on the "type of cancer," not the "breed." Research shows the mutation patterns that drive tumor growth are broadly similar across breeds (tumor type-dependent, but largely breed-independent). Even though some breeds carry genetic tendencies that make cancer more likely, the actual mechanism of malignancy is a cellular-level accident unique to each individual dog.

One of the most frequently mutated genes across all canine tumor types (in up to around 22.5%) is TP53, the body's main tumor suppressor gene. When this gene is damaged at the somatic (body-cell) level, the control system for cell division breaks down and a malignancy can eventually form. If you'd like the bigger picture of which inherited diseases are common in each breed, read more in common genetic diseases by dog breed.

Dogs as a "Model" That Helps Both Dogs and Humans

Did you know that cancer in dogs resembles cancer in humans to a remarkable degree, in terms of genetic defects, disease progression, and arising spontaneously (spontaneous malignancy) in animals with a fully intact immune system? Dogs also share our environment and risk exposures, and with their much shorter lifespan they serve as an "accelerated" model that yields answers faster than human studies (Bird & Smith, Veterinary Sciences, 2025).

This resemblance lets scientists use canine cancer genetics as a model for clinical (translational) research. The results not only lead to new cancer treatments for humans but also feed back into more effective, targeted therapies for dogs, giving them better care with less pain. This is "One Health" in action.

What DNA Can and Can't Tell You

Canine DNA testing today is therefore not about "labeling" a dog as destined for cancer. It is about helping you understand your dog's individual tendencies and risks, so you can plan preventive care, avoid triggers, and monitor health precisely and early, because the earlier something is caught, the higher the chance of controlling it.

The key point I want to emphasize is that finding a risk variant does not mean your dog will get cancer. Genetic risk is an association, not a cause and not a destiny. Environment, age, and cellular chance all play a large role too. Knowing your dog's breed and genetic background is simply a good starting point. Read more about DNA breed identification in dogs, and if you'd like to understand care when cancer is suspected, see our owner's guide to cancer in dogs.

Genetic test results are only an advance risk assessment, not a diagnosis. If you notice anything unusual or any lump on your dog, please take them to a veterinarian for a thorough examination.

References

1. We need to rethink the genetics of cancer in dogs. Beuchat CA. The Institute of Canine Biology. 2025. instituteofcaninebiology.org
2. Bird RC, Smith BF. Comparative Genetics of Canine and Human Cancers. Veterinary Sciences. 2025;12(9):875. NCBI PMC