Matthew Breen, Professor of Genomics and the Oscar J. Fletcher Distinguished Professor of Comparative Oncology Genetics at North Carolina State University’s College of Veterinary Medicine, says he invariably gets questions when he gives talks on the subject of human and dog health from (apparently dogless) experts in human medicine. “Wait a minute, you’re saying that dogs get cancer? And people pay to have them treated?” The answers, of course, are “yes, indeed” and “sometimes, yes.”
Decisions about medical treatment for beloved pets inevitably depend on many factors, such as their age, degree of suffering, and chances of recovery. As much as many people love their pets, cost is a factor. Most people don’t have pet insurance to help them pay for expensive surgery, chemotherapy, or other medical treatments. But, Breen says, veterinary medicine has come a long way.
“Using the dog genome sequence in combination with the human genome sequence will help researchers to narrow their search for many more of the genetic contributors underlying cancer and other major diseases.”
In the past, veterinarians may have spent the vast majority of their time neutering, spaying, and vaccinating dogs and cats. While those activities are still a much-needed mainstay of most general-practice veterinary clinics, Breen says, there are “now thousands of specialized clinicians: veterinary oncologists, neurologists, ophthalmologists, dermatologists, and behaviorists, etc. I think many people don’t realize just how sophisticated the veterinary profession is. The quality of care at places like [NC State] is world class.”
At NC State, as at other major veterinary hospitals, dogs and other animals have access to MRI scans, prosthetic limbs, and the cancer treatments, including chemotherapies, that are deemed most appropriate for their cancer type. Breen says there is more progress still to be made when it comes to personalizing pet therapy, but veterinary medicine is following a pattern roughly similar to that in human medicine. In the past, for example, women with breast cancer were all treated more or less the same, with little regard to the particulars of their cancer, he says. These days, doctors are increasingly looking deeper and selecting among treatment options based on a variety of factors.
“Our animal companions benefit from exactly the same approach in veterinary medicine,” Breen says. Not all dogs with the same condition are treated in the same way.
Charles Swearingen and his wife, Pam, learned of Breen and his work last year after their Bernese mountain dog named Hannibal, who traveled all over the country with them and slept on their bed curled up like a doughnut, started showing some odd behaviors. Hannibal was looking “lackluster,” sitting in corners and staring at the wall. The first ultrasound showed a mass, and the vet thought it might be prostate cancer. A second scan looked even more ominous, but the biopsy came back inconclusive. Finally, Hannibal’s tumor sample made it to Breen’s lab at NC State, where a genomic test and pathology report confirmed a diagnosis of T cell lymphoma.
Many dog breeds, including “Berners” like Hannibal, have a high incidence of lymphoma. Left untreated, dogs with lymphoma rarely survive for more than a couple of months.
Breen has identified genetic factors for dogs diagnosed with lymphoma, that can help to predict how long a dog is likely to respond to standard-of-care chemotherapy. Without the test, the best a vet might be able to say is that a dog has a fifty-fifty chance of living for nine months with a treatment that could be difficult and costly to pursue. With the test, Breen says, it’s possible to predict a particular dog’s likelihood of response with much greater certainty. In Hannibal’s case, the test predicted a 90 percent chance that Hannibal would still be in remission at seven months, but he had a much lower chance by nine months. The Swearingens opted for treatment.
“Matthew mentioned that this was good for research for the breed, which is something we cared about,” Charles Swearingen says. “At the same time, it was a benefit for us. It helped us realize we had a chance for a good remission, so we should push ahead and get Hannibal whatever we could.”
Hannibal did indeed perk up with treatment for months, giving the family more time together. During that time, Hannibal and the Swearingens welcomed a new Berner puppy called Gus into their home. With Hannibal’s health deteriorating again, the Swearingens realized it was time to say goodbye in November 2014, about eight months after the initial diagnosis.
While Breen spends most of his time with veterinary patients, he isn’t thinking only of our pets. If his lymphoma test or others like it are developed and shown to work in dogs, they might be adapted, or “humanized,” for use in people with the same disease. That’s the whole premise of the quickly expanding field of comparative oncology, of which Breen is one of the major proponents — to study cancer across species with the goal to advance both human and animal health. Breen considers cancer to be “low-hanging fruit,” but the approach is applicable to other diseases as well. Human and dog health are in many ways, he says, “opposite sides of the same coin.”
The fact that dogs and humans suffer from many of the same health conditions is something Breen has appreciated from the time he was young. When he was a child, an important canine member of his family fell ill. It was cancer and, according to the vet at the time, there was really nothing to be done except let her go peacefully. It was this early heartbreak that convinced him to pursue veterinary health in the first place. When vet school didn’t quite pan out, he switched gears to pursue genetics, while maintaining his focus on veterinary patients. He soon began to realize that many of the tools used to study cancer in humans could also be applied directly to other animals, dogs included.
As he looked at cancer in dogs more closely, he started to realize something else. Dogs don’t just get the same basic types of cancer that people do. Their cancers also look very similar to human cancers in terms of their clinical presentation and other features. In the mid-1990s, he began to examine biopsied tissue taken from the lymph nodes of dogs with lymphoma. On a whim, he once sent a sample of non-Hodgkin lymphoma from a 6-year-old Rottweiler to a human pathologist, without mentioning where the sample had come from. The pathologist called to say it was a fascinating case; he’d never seen such an aggressive cancer of that sort in a child so young. Breen realized he’d left in the age of the dog, but the human pathologist was amazed at the level of similarity with his own patients.
“At the cellular level, it’s not that easy to tell the difference between them,” Breen says. He started to make more detailed comparisons between human and dog cancers and discovered that, in nearly every case, the diseases in both species involved some of the very same kinds of chromosomal rearrangements. Breen believes that identifying these shared changes is key to discovering the drivers of cancers across species.
“Many of the changes in canine lymphoma were exactly the same as in corresponding human patients,” Breen says. “It drove home to me that these are our best friends, and they really are not that different from us.”