Inheritance, risk factors and breeding considerations of cancer in dogs

Katariina Mäki, PhD

Cancer is usually an age-related disease. Age-related cancers are often caused by genetic mutations that are not passed on to offspring. The development of early-onset cancers, on the other hand, is more likely to be influenced by inherited genetic changes. A variety of mechanisms may underlie hereditary cancer susceptibility. In some dog breeds, it may be a single genetic mutation that causes a particular type of cancer.

Flat-Coated Retriever. Photo: Walter Bieck, Pixabay

What are common types of cancer in dogs?

Some common types of cancer in dogs include:

Lymphoma/Lymphosarcoma: A proliferation of cancerous lymphoid cells in the lymphatic system.
Mast Cell Tumors: The most common type of skin tumor in dogs, which can also affect other areas of the body.
Mammary Tumors: Common in intact (un-spayed) females, with a higher incidence in certain breeds.
Osteosarcoma (Bone Cancer): The most common type of bone cancer in dogs, which tends to spread rapidly and is more common in giant breeds.
Hemangiosarcoma: A highly aggressive cancer that affects the lining of blood vessels and commonly occurs in the spleen, heart, or liver.

These types of cancer can have varying symptoms and treatment options, and understanding the specific type of cancer is crucial for effective management and care.

Risk factors for developing cancer in dogs

Some risk factors for developing cancer in dogs include:

Age: Older dogs are more susceptible to developing cancer.
Genetics: Certain breeds have a higher predisposition to specific types of cancer due to inherited genetic mutations.
Environmental Factors: Exposure to environmental contaminants like cigarette smoke, asbestos, pesticides, herbicides, and other toxins can increase the risk of cancer in dogs.
Nutrition: Dietary factors, such as obesity and specific food choices, can impact the likelihood of cancer development in dogs.
Sun Exposure: Dogs with light pigmentation are at higher risk of cancer from sun exposure, especially if they are not protected from harmful UV rays.
Hormones: Intact female dogs and cats can have an increased risk of mammary adenocarcinoma, but on the other hand, spaying/neutering is a risk factor in some dog breeds.
Lifestyle Choices: The presence of smoking in the household has been associated with an increased risk of nasal cancer, particularly in long-nosed dog breeds such as Labrador Retrievers and Collies. Additionally, there is a correlation between smoking in the household and an elevated risk of lung cancer in brachycephalic dogs.

Which dog breeds are at an increased risk of developing cancer?

Cancer has been estimated to cause 15-27% of all deaths in pedigree dogs. Schifman and Breen (2015) estimate that cancer incidence in dogs is ten times higher than in the human population.

Cancers occur in both pedigree and mixed-breed dogs. Some breeds have a higher-than-average risk of cancers, especially certain types of cancer, which is a sign of heredity.

For example, early-onset and life-shortening histiocytic sarcoma occurs in Flat-Coated Retrievers and Bernese Mountain Dogs (Dobson 2013, Ostrander et al. 2019, Rowell et al. 2011). Histiocytes are a type of white blood cell. When a dog develops histiocytosis, these cells proliferate abnormally and invade different tissues.

Histiocytic sarcoma also occurs in Rottweilers and Golden Retrievers (Affolter and Moore 2002, Shaiken et al. 1991, Hayden et al. 1993, Hédan et al. 2021).

Irish Wolfhounds are prone to bone cancer — Irish Wolhound. Image by DejaVu Designs on Freepik

Abdominal cancer has been reported in Belgian Shepherds (Scanziani et al. 1991).

Irish Wolfhounds, Scottish Deerhounds, Great Danes and other giant breeds are at hereditary risk for aggressive bone cancer (osteosarcoma; Letko et al. 2021, Momen et al. 2021, Phillips et al. 2007).

Brain and central nervous system cancers occur particularly in Boxers, Golden Retrievers, French Bulldogs, Boston Terriers and Rat Terriers, according to a study by Song et al (2013).

Schifman and Breen (2015) provide a comprehensive table of cancer types associated with different dog breeds.

What is known of the number of cancer deaths in different dog breeds?

In a Swedish study by Bonnett et al (1997), the highest number of cancer-related deaths was found in the Bernese Mountain Dog, Irish Wolfhound, Flat-Coated Retriever, Boxer and St.Bernard. 

In a later study from the same database, the top breeds were the Bernese Mountain Dog, the Irish Wolfhound and the Leonberger (Bonnett et al. 2005).

The Bernese Mountain Dog, the Flat-Coated Retriever, the Golden Retriever and the Rottweiler were the four breeds with a cancer death rate in Denmark of more than 20% (Proschowsky et al. 2005).

In a British study by Adams et al (2010), the top five were the Irish Water Spaniel, Flat-Coated Retriever, the Wirehaired Vizsla, the Bernese Mountain Dog and the Rottweiler (Table 1). The Adams study also examined the average age of cancer deaths, which was lowest in English Bulldogs and Leonberger dogs.

Information search provided also these results:

Golden Retrievers – Prone to lymphoma, hemangiosarcoma (cancer of the blood vessels), and other aggressive forms of cancer. Studies have identified genetic factors that may contribute to their higher cancer risk.
Flat-Coated Retrievers have high incidence of histiocytic sarcoma and lymphoma. Their cancer susceptibility is believed to be largely genetic. Up to half of all Flat-Coated Retrievers will develop cancer by the age of 8, with many dying from the disease.
German Shepherds – Commonly develop hemangiosarcoma (cancer of the blood vessels).
Beagles – Have a higher risk of developing bladder cancer, lymphoma, and osteosarcoma (bone cancer), especially in older dogs.
Bernese Mountain Dogs – Susceptible to a variety of cancers including malignant histiocytosis (histiocytic sarcomas) and mast cell tumors. They also have one of the shortest average lifespans among dog breeds.
Rottweilers – At high risk for developing soft tissue sarcomas, osteosarcoma (bone cancer), lymphoma, mast cell tumors, transitional cell carcinomas (bladder cancer), and hemangiosarcomas.
Boxers – Prone to mast cell tumors, a type of slow-growing skin cancer.

Other breeds mentioned as having increased cancer risk include Great Danes, Poodles, Cocker Spaniels, Doberman Pinschers, and certain terrier breeds like Scottish Terriers.

How can I reduce my dog’s risk of developing cancer?

To reduce your dog’s risk of developing cancer, you can take several proactive steps based on the information provided in the sources:

Provide a Healthy, Balanced Diet: Ensure your dog receives a well-balanced diet that meets their nutritional requirements.
Maintain a Healthy Weight: Manage your dog’s weight through proper diet and exercise to reduce the risk of certain cancers associated with obesity.
Avoid Environmental Risks: Minimize exposure to harmful substances like asbestos, lawn chemicals, and secondhand smoke, which can increase the risk of cancer in dogs.
Regular Dental Care: Implement a robust dental care routine to lower the risk of oral cancer in dogs.
Avoid Toxic Chemicals: Opt for natural alternatives to flea and tick products containing harmful chemicals, and maintain a chemical-free environment to reduce cancer risk.
Limit Sun Exposure: Protect dogs with light pigmentation from excessive sunlight exposure and use dog-safe sunscreen to reduce the risk of skin cancer.
Regular Veterinary Check-ups: Schedule routine physical examinations with a veterinarian for early detection and treatment of any potential health issues, including cancer.
Sterilization: Sterilization can be considered as a preventive measure against certain types of cancer, such as mammary cancer in female dogs, but this is not true for all breeds. For example in Golden Retriever females, sterilization is a risk factor for cancer (Hart et al. 2020). Nevertheless, it is advisable to avoid spaying the dog prematurely, and to only proceed with this procedure once the animal has reached adulthood.

By following these guidelines and incorporating them into your dog’s daily care routine, you can significantly reduce the risk of cancer and help your furry companion lead a healthier and longer life.

Is cancer in dogs hereditary?

Cancer is usually an age-related disease (Bonnett and Egenvall 2010). Age-related cancers are often caused by genetic mutations that are not passed on to offspring. The development of early-onset cancers, on the other hand, is more likely to be influenced by inherited genetic changes (Nunney 2013).

Cancer inheritance in dogs can be influenced by genetic factors and breed predispositions. While most cancers in dogs are caused by spontaneous mutations that occur during a dog’s lifetime, certain breeds have a higher incidence of specific cancers due to inherited genetic mutations.

These mutations can enhance the risk of developing cancer in dogs, and understanding these genetic factors enables veterinarians and researchers to identify high-risk breeds and develop targeted prevention and treatment strategies.

Additionally, the limited genetic diversity in purebred dogs allows for the elucidation of the genetics behind various cancers, aiding in the identification of genes associated with increased cancer risk and the development of tests to help avoid breeding dogs with these “bad genes”.

Mode of inheritance of canine cancers

A variety of mechanisms may underlie hereditary cancer susceptibility. In some dog breeds, it may be a single genetic mutation that causes a particular type of cancer.

For example, renal cancer syndrome in German Shepherds is a rare disease inherited with a dominant genetic mutation (Lingaas et al. 2003). In humans, a similar disease is known as Birt-Hogg-Dube syndrome.

Cancer susceptibility may also be linked to a hereditary dysfunction of growth restriction genes that inhibit the formation of cancer cells, which strongly predisposes to several different types of cancer occurring at a young age. In dogs, examples of concurrent tumours in different parts of the body are also known (Nakagawa et al. 2009 and Rebhun and Thamm 2010). In humans, such dysfunction is for example the rare Li-Fraumen syndrome, which is inherited in a dominant manner.

The genetics of hereditary cancer may also resemble human BRCA1 gene mutations, which cause susceptibility to the disease. The risk of developing cancers such as breast and ovarian cancer is higher in relatives of those affected, rather than the straightforward inheritance of a particular cancer. Rivera et al (2009) showed a significant association between mutations in the BRAC1/2 genes and mammary gland tumours in English Springer Spaniels.

For canine osteosarcoma, heritabilities have been estimated:

Irish Wolfhound 0.65 (Momen et al. 2021)
Scottish Deerhound 0.69 – The mode of inheritance was proposed to be a dominant major gene (Phillips et al. 2007).
Leonberger 0.21 – The prevalence of osteosarcoma in this study was 20% (Letko et al. 2021).

The mode of inheritance of histiocytoma has been suggested to be polygenic (Padgett et al. 1995 and Abadie et al. 2009) and the heritability has been estimated to be 0.30 in Bernese Mountain Dogs (Padgett et al. 1995a). Many other types of cancer are also likely to be polygenic.

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Does a genetic test for cancer exist in dogs? If not, how might one incorporate cancer into breeding considerations?

There are a few key points regarding genetic testing for cancer in dogs and considerations for breeding:

Genetic testing for cancer predisposition in dogs is still an emerging field, but some tests are becoming available:

Panel tests can in the future evaluate genes associated with certain hereditary cancers in dogs, but these tests are not yet widely available.
Specific genetic tests are available for certain cancer predispositions, like the BHD gene test for renal cystadenocarcinoma and nodular dermatofibrosis in German Shepherd dogs.
More research is needed, but the development of genetic tests to identify dogs at high risk for cancer is an important goal for the future.

Many cancers in dogs are thought to be non-hereditary, caused by spontaneous mutations rather than inherited genetic factors. However, certain breeds do show a higher incidence of specific cancer types due to genetic predispositions.

When considering breeding, it is important to:

Avoid breeding dogs affected with known hereditary cancer predispositions, as they have a 50% chance of passing the mutation to offspring.
Use available genetic tests to screen for cancer-associated mutations and avoid breeding dogs that test positive. Especially avoid combining two dogs that have both tested positive.
Be aware of the increased cancer risks in certain breeds and consider this when making breeding decisions, even without a specific genetic test. This requires information sharing and collaboration among dog breeders and owners. Do not combine two dogs with greater than breed’s average risk for cancer.
Maintain genetic diversity in the breed to reduce the prevalence of inherited cancer susceptibilities.

In summary, while comprehensive genetic testing for cancer in dogs is not yet widely available, breeders should stay informed on the latest research and utilize information sharing, breed databases and any relevant genetic tests to make responsible breeding decisions that minimize the risk of passing on inherited cancer predispositions to future generations.

References

If you’re interested in a certain study mentioned in the article, please ask for the reference by commenting below.