Companion animals and their owners usually face very different medical concerns. While humans rarely worry about developing kennel cough and pets have no concern of catching chickenpox, cancer is unique in that nearly every species can develop it and that it may present similarly across species lines.
Dr. Shay Bracha, an associate professor at the Texas A&M College of Veterinary Medicine & Biomedical Sciences, says that 1 in 3 dogs and 1 in 4 cats will be diagnosed in their lifetime with cancer, compared to 1 in 5 humans diagnosed.
In addition to chemotherapy and radiation, humans may receive targeted therapies that are not widely available to animals, a result of extensive research into drugs that effectively fight specific types of cancer. However, Bracha says that veterinary researchers are working to develop similar targeted therapies for animals.
In the meantime, most pets are treated with the same chemotherapy drugs or radiation humans receive.
“We do use many of the same medications—same drugs, same chemotherapy, radiation, and so on—to treat animals that we use in human medicine,” Bracha said. “So, many of the medications are pretty much the same. The differences are in the dose and the frequency that we give our animals versus humans.”
Animals receive more conservative doses to reduce toxicity and side effects, since pets can’t communicate with their doctor the same way a person can. Oftentimes, this lower dose leads to fewer side effects from treatment, such as decreased nausea, diarrhea, and bone marrow suppression.
Unrelated to treatment dose, Bracha says that most pets won’t lose their fur during chemotherapy, as animal fur doesn’t grow continuously like human hair does. However, some breeds that grow hair instead of fur, such as poodles, might still lose their fluffy coat.
Like humans, pets may also be affected by similar mutagens, or cancer-causing agents, such as air pollution, and pets living in polluted urban areas may be at higher risk for certain types of cancers as a result of their environment.
“There’s enough evidence for other cancers that are associated with mutagens. For example, specific herbicides and pesticides are known to be linked to bladder cancer in dogs,” he said. “Dogs that live in rural areas and run into fields that have been sprayed with an herbicide can develop bladder cancer at a higher frequency than dogs that don’t live in this environment”
Certain breeds may also carry genetic risks for certain types of cancers, as well. For example, terriers are at higher risk for bladder cancer than other breeds. Large dog breeds also tend to have higher rates of osteosarcoma, or bone cancer, than smaller breeds.
In addition to the shared phenomenon of genetic risk, canine cancer often develops very similarly to human cancer.
“The progression of osteosarcoma is very, very similar between humans and animals,” he said. “They start in the same locations in the body, they metastasize to the lungs, and they oftentimes have a very aggressive course of disease.”
Other forms of cancer, including bladder cancer, Non-Hodgkin’s lymphoma, and soft tissue sarcomas, also share similarities between the two species.
Canine cancers are so similar to human malignancies that the National Institutes of Health (NIH) has designated research into canine cancers a priority, using them as a model for human cancers to improve treatment outcomes in both species.
“Our pets live with us and, therefore, are exposed to the same toxins and environmental stressors, which makes the disease closer to their human counterparts,” he said. “There are a lot of efforts to learn new therapies in the dog and try to move with that model to the human side of healing.”
Although cancer is a tragic disease in both our furry friends and their human owners, veterinary and medical researchers are working hard to better understand this disease and develop a more effective fight against it. In the coming years, we can look forward to more targeted and effective therapies for humans and pets alike.
Pet Talk is a service of the College of Veterinary Medicine & Biomedical Sciences, Texas A&M University. Stories can be viewed on the web at vetmed.tamu.edu/news/pet-talk. Suggestions for future topics may be directed to firstname.lastname@example.org.