From Breed to Environment: Key Risk Factors for Canine Cancer
For many pet owners, "the big C" is the ultimate bogeyman, sparking fear of losing their beloved companion too soon. By understanding risks affecting our patients, we can better educate clients, perform appropriate screening, and facilitate early diagnosis—key steps in achieving the best possible outcomes.
For as much as we talk about cancer in both medical practice and day-to-day conversation, it is a surprisingly hard word to define. At its core, cancer is a group of several hundred diseases that are characterized by unregulated cell growth, as well as the invasion and spread of these cells to other sites within the body.
Here's what to know about cancer risks affecting dogs.
Cancer Is a Genetic Disease
Understanding why some animals are more prone to cancer begins with understanding the underlying cause of the disease, and how tumors form. Cancer is fundamentally a genetic disease. The mutations underpinning tumors can arise from:
- Errors in DNA replication during cell division
- DNA damage from chemical, physical, or biological factors
- Inherited mutations
Common causes of DNA damage include:
- Chemical factors: Tobacco smoke, pesticides, and other environmental pollutants
- Physical factors: UV radiation from sunlight, trauma, and surgical implants (e.g. TPLO plates with osteosarcoma)
- Biological factors: Viral infections (e.g. FeLV in cats), and reproductive hormones
Risk Increases With Age
While cancer can occur at any age, risk increases with age. Over time, cumulative exposure to DNA-damaging agents and replication errors introduce mutations that increase the likelihood of tumor development. A study involving over 3,000 dogs found that the median age of diagnosis was approximately 9 years. This study also showed the median age at diagnosis varied with both breed (boxers and bulldogs were diagnosed at significantly younger ages than other breeds) and with malignancy type (diseases like lymphoma and mast cell tumors typically appeared earlier than other tumors).
Breed Is Associated With Cancer Risk
It may not be surprising to learn some breeds have an increased risk of cancer. Purebred dogs generally appear predisposed to cancer at younger ages compared to their mixed-breed counterparts. This same study noted some breeds were relatively younger at the time of diagnosis with a median age of 5-7 years, including mastiffs, Saint Bernards, Great Danes, bulldogs, Irish wolfhounds, boxers, vizslas, and Bernese mountain dogs. For comparison, mixed-breed dogs were diagnosed at a median age of 9 years. A study of purebred dogs in the UK reported cancer mortality rates of 45-55% in Irish water spaniels, flat-coated retrievers, Hungarian wirehaired vizslas, Bernese mountain dogs, and Rottweilers, compared to 25% across all breeds.
Beyond this general risk, there are also breeds with well-established risks of specific malignancies. These include the risk of urothelial carcinoma (also known as transitional cell carcinoma) in the Scottish terrier, the risk of histiocytic sarcoma in Bernese mountain dogs and flat-coated retrievers, and the risk of osteosarcoma in giant breed dogs (including Irish wolfhounds, Great Danes, and greyhounds).
Environmental Factors Influence Cancer Risk
Environmental exposures also influence cancer development. However, it can be challenging to definitively correlate exposure to an environmental carcinogen with tumor development. This is because true exposure is difficult to quantify, and a large sample of animals must be evaluated to detect subtle effects. As such, multiple known carcinogens in humans including radon, tobacco smoke, and pesticides/herbicides/insecticides have all been evaluated with often inconclusive results. Several studies have linked exposure to tobacco smoke with lymphoma in cats, and with nasal tumors in dolichocephalic dog breeds. Additional studies have linked exposure to environmental waste with increased incidence of lymphoma in dogs. Further, studies have linked a higher incidence of urothelial carcinoma with exposure to pesticides in Scottish terriers, and with chlorination byproducts (in tap water and swimming pools) in canines of all breeds.
Sun exposure is also linked to several skin cancers, including cutaneous hemangiosarcomas, particularly on the ventrum of dogs. This risk is amplified in areas of the country with higher UV levels.
Identifying High-Risk Patients
Early diagnosis improves outcomes and saves lives, and understanding risk is the first step in early diagnosis. Identifying high-risk patients based on age, breed, and environmental factors enables veterinarians to:
- Educate pet owners about their pet's specific risks
- Recommend appropriate screening schedules and wellness visits
- Tailor diagnostic and preventive care strategies
Proactive management not only improves survival rates—as pets get the care they need more quickly—but also enhances quality of life for pets and peace of mind for their owners.
