Why dogs are the key to treating human cancer

Cancer is a cruel disease that affects large swaths of the animal kingdom. Few creatures are spared — not even man’s best friend.

But as it turns out, this deadly link between dogs and humans could also save us. Researchers recently discovered certain genes are linked to a rare form of cancer in certain dogs. These findings could also potentially help scientists better understand how this cancer also manifests in humans, argues a study published Thursday in the journal PLOS One.

What’s new — In the study, scientists identify two genetic risk factors that, together, account for 35 percent of a Flat-Coated Retriever’s risk for histiocytic sarcoma — a rare, lethal blood cancer.

Flat-Coated Retrievers are a sporting dog known for their happy attitude, energy, and lustrous black coat.

The genetic risk factors are two loci — a gene’s specific location on a chromosome — known as CFA5 and CFA19. According to the researchers, CFA19 “has not been previously associated with cancer risk.”

The researchers also found CFA5 is associated with two other cancers apart from histiocytic sarcoma: hemangiosarcoma and B-cell lymphoma.

The researchers specifically studied this cancer in Flat-Coated Retrievers, which have a high overall risk factor for the disease. Approximately 20 percent of Flat-Coated Retrievers ultimately become diagnosed with the disease.

It’s not entirely clear whether these findings can apply to other dog breeds, too. However, another study published earlier this year found that Bernese mountain dogs, Rottweilers, and retrievers carrying certain genes with certain loci had five times greater risk of developing histiocytic sarcoma.

What are the cancers found in dogs?

Dogs, like humans, experience a range of cancers that can occur in different parts of their bodies. Roughly 6 million dogs — or one in four pups — get cancer each year, according to the National Cancer Institute.

Histiocytic sarcoma is an aggressive but rare cancer that occurs later in a dog’s life. Dogs with this type of cancer don’t typically live long after diagnosis.

But there are also more common cancers in dogs. These include:

• Bone cancer
• Lymphoma
• Mast cell (skin cancer)
• Mammary tumors (breast cancer)
• Hemangiosarcoma (tumors lining blood vessels)

One of the most common of these cancers is lymphoma: Approximately 20 percent of canine cancers are linked to lymphoma.

How are cancers in dogs treated?

After a dog is diagnosed with cancer, they receive many of the same treatment options as humans, including:

• Surgery
• Chemotherapy
• Radiotherapy

As with humans, the treatment plan will depend on the type of cancer and the pet’s current health.

However, the researchers in this study suggest another method to prevent, rather than treat, cancer in dogs: selective breeding.

The study authors note how selective breeding has increased the risk of cancer in Flat-Coated Retrievers. Humans selectively breed retrievers for traits like the length of the dog’s muzzle, but this breeding practice unintentionally increases the frequency of cancer genes in the dog’s gene pool.

“In general, breeders choose [to] mate pairs they believe will produce healthy puppies with the behavioral and physical traits that characterize the breed,” lead author Jacquelyn Evans, a postdoctoral research associate at the National Human Genome Research Institute, tells Inverse.

“However, with late-onset cancer like histiocytic sarcoma, dogs are bred well before they show any signs of disease themselves, and it can be nearly impossible to predict whether a given set of parents will have offspring that eventually develop cancer,” Evans says.

Evans and colleagues argue for using selective breeding to reduce the risk of these cancer genes appearing in the gene pool over time. Evans explains how their findings can help dog breeders:

“Knowing the genetic risk factors involved in histiocytic sarcoma in flat-coated retrievers means a genetic test could be developed to provide breeders with more information, if they choose, to carefully reduce the risk of this cancer.”

An ongoing trial known as the Vaccination Against Canine Cancer Study — the largest clinical canine cancer trial ever conducted — also seeks to prevent the growth of cancer in dogs, albeit through vaccines, not breeding methods. The scientists behind that study also hope they can apply their findings to help human cancer patients.

How does dog research help human cancer patients?

Scientists have long known dogs can serve as good models for studying cancer in humans. That’s partly because cancer presents in a similar fashion in both dogs and humans, and safe cancer treatments in dogs often work well in humans, too. But it’s also simply easier to study the progression of genetic diseases in dogs because of their shorter lifespans and the fact selective breeding reduces the complexity of a breed’s gene pool.

The researchers behind the PLOS One study write that dogs serve as an “excellent model for genetic studies of cancer susceptibility.”

The researchers also note that late-onset cancers, like histiocytic sarcoma, have traditionally been difficult to study in humans due to the late diagnosis. However, since scientists have been able to research the genetic origins of blood cancer in dogs, there may be hope for human research as well.

“Because dogs closely model the human disease, we expect overlap in the genes that are important for canine and human histiocytic sarcoma, and our study identified pathways that are impacted in some human tumors,” Evans says.

There’s another way that our pups can be helpful: Now that we’ve identified genetic risk factors for cancer in dogs, we could potentially identify them in humans and develop treatments as a result.

“Understanding the genes involved in histiocytic sarcoma can lead to the use of therapies that block cancer progression by directly targeting those genes or the pathways in which they function,” Evans says.

In turn, humans might be able to help our loyal companions, too. In recent years, scientists have begun exploring various treatments — previously reserved for humans — in dogs with cancer.