Humans have a research bond with their canine friends.
Purebred Dogs
Thinking of a dog helping cure cancer likely brings images of golden retrievers sniffing blood samples of Scottish terriers lying next to a cancer specimen. Undoubtedly, their noses are fantastic, but the secrets are often inside the purebred pups. It is their tumors scientist study. Approximately 25% of purebred dogs die of cancer. Roughly 45% of those over 10-years old die from one variety or another.
Some pups actually get modern chemotherapy treatment just like people. In many cases, those options work because the canine cancers are so close to human tumors.
“For the most part, dogs get everything we do,” Elaine Ostrander, a distinguished investigator at the National Institutes of Health and chief of its Cancer Genetics and Comparative Genomics Branch, suggested. “You see some striking similarities that you don’t see in mice or other animal models, and that makes them an increasingly terrific system to study the genetic basis of disease.”
Dogs are excellent disease models because they happen to get the same cancers. Additionally, they are genetically like one another. Why? Because we’ve bred them that way.
Susceptibility
In short, most purebred dogs are so inbred that we might as well be mating siblings. The offspring of two siblings have an inbreeding coefficient of 0.25. Additionally, most of the possible purebred pairing has a coefficient above that mark.
This is horrific for disease risk since otherwise rare disorders can quickly become expected when you have a small, closed gene pool. It is excellent if you want to study cancer genetics. The heritage of an animal can make them more susceptible to specific cancers.
“If you’re a Scottish terrier, your odds of getting bladder cancer are 22 times higher than your average mutt,” explained Ostrander.
The risk is massive because people have taken a set of inherited mutations and inadvertently bred it into the group. This, however, makes them an ideal sample group for research.
Humans are usually too genetically varied to trace cancers back to inherited mutations. Roughly 55 percent of cancers are not habit-related, like BRCA mutations for breast cancer and APC mutation for colorectal cancer, which are the most famous. When the mutation shows a solid familial disease pattern, you can look at a small, genetically similar group like a family. For humans, modern sequencing methods make it easy to pick out which gene or genes have the mutation.
Purebred Dogs
Since all purebred dogs are related to one another, every cancer they get is similar to the hereditary human cancers known to scientists. For example, digit squamous cell carcinoma is widespread among a few select breeds: giant schnauzers, Gordon setters, Briards, Kerry blue terriers, and black standard poodles. These breeds are prone to squamous cell cancers because they carry the same founder mutation— it produces too many copies of the gene KITL.
Not all dog cancers stem from a founder mutation. Some seem to have a shared susceptibility.
Bone Cancers
Osteosarcomas, to clarify, are a type of bone cancer that is relatively rare in humans. Many long-limbed breeds—Irish wolfhounds, Great Danes, and Scottish deerhounds—get them frequently. This is likely due to a shared genetic heritage for long legs, giving them a shared predisposition to the disease.
As a result, researchers decided to see whether these dogs had mutations in common. As it turns out, they often have mutations in two genes called IL-8 and SLC1A3, both known to cause some of the more malignant forms of human osteosarcoma. Consequently, scientists can focus on those two genes to determine precisely how osteosarcoma forms and its progression.
Ostrander’s group focuses on three other diseases: gastric cancer, histiocytic sarcoma, and bladder cancer. “We’ve been interested in bladder cancer because a small number of breeds are at super high risk,” she explained, “and gastric cancer because it’s so lethal in both humans and dogs. In humans, it’s months from diagnosis to death. In dogs, it can be a few days to weeks.” Both types of cancer affect certain breeds to a high degree but don’t appear in most other dogs.
Histiocytic sarcoma, third cancer in Ostrander’s focus group, is rare in humans. But 25% of the Bernese mountain dogs and 20% of flat-coated retrievers get it. These cancers start in the blood cells, which developed separately in each breed. Despite being the same cancer, the disease patterns differ. Bernese get tumors in the spleen, lungs, and liver, while retrievers get it in joints and muscles.
This isn’t so useful for humans since it’s such a rare form of cancer. It helps understand how cellular mutations affect disease evolution. Two breeds, same cancer, yet finding the differences can isolate the disease’s progression for solutions.
“We’ve been fascinated by that,” Ostrander said, “because we know it’s different genes for Bernese and flat-coated retrievers.” With more study, those genes might prove crucial in directing which bits of the body are most susceptible to cancer.
Hopeful Research
As a result, the hope is purebred puppy studies will unlock novel ways to treat human cancers. For example, mouse models of cancer often don’t help test new therapies because cancer is induced for research and doesn’t mutate naturally. Dogs, on the other hand, get these cancers naturally—or as naturally as an inbred population can get them.
This means the dog cancer treatments that do work often work in humans. It is excellent news. Rather than giving a creature cancer, dogs already have cancer. Therefore, research will help dog outcomes along with people.