Risk Factors for Canine Lymphoma

Several studies have examined relative risks for lymphoma development in dogs due to breed, sex, and reproductive status. Researchers at the University of Sydney School of Veterinary Science in Australia recently performed a large-scale study to investigate these factors in the country’s pet dog population.

Methods

Patient records were retrieved from 2 referral hospitals, a commercial veterinary diagnostic laboratory, and a general veterinary practice in Australia. From these, investigators identified dogs with cytologically or histologically confirmed lymphoma or lymphosarcoma.

They then compared population statistics of dogs with lymphoma with a reference dog population in Australia by obtaining signalment information (breed, sex, and neuter status) for dogs presenting to 3 referral hospitals in the country. Additionally, they requested signalment data of registered dogs from local councils throughout the country. Dog registration is mandatory in certain regions of Australia.

RELATED:

• ACVP 2017: Test-driving CARs to Treat Canine Lymphoma
• Feline Lymphoma: How Has It Changed?

The authors used the data to determine the 50 most popular dog breeds in the reference population, as well as any breed with either 10 or more cases of lymphoma or a documented increase or decrease in lymphoma risk. From this information, they calculated odds ratios for breed, sex, and neuter status for prevalence of lymphoma.

Results

• Cases of lymphoid neoplasia included:
• 1265 dogs presenting to referral hospitals
• 4040 cases at the diagnostic laboratory
• 896 cases in general practice

Information was compared with that of a reference population of 640,105 dogs in Australia. A total of 205 purebreeds and 195 crossbreeds were identified.

Of 78 breeds evaluated for lymphoma risk, 30 were found to have a higher than average risk for lymphoma development, while 26 had a decreased risk. Interestingly, none of the top 5 breeds with increased lymphoma risk in the study (Dandie Dinmont terrier, foxhound, Chesapeake Bay retriever, Neapolitan mastiff, and mastiff) had a previously identified risk. Also, several breeds previously documented to have an increased risk of lymphoma failed to show an increased risk here. Compared with purebred dogs, crossbreeds generally had a decreased risk of lymphoid neoplasia; still, crossbred dogs accounted for 28% of lymphoma cases in the study.

In general, male dogs had a higher risk for lymphoma compared with females, especially for the boxer and cocker spaniel breeds and crossbred dogs. In contrast, female bulldogs and Dogue de Bordeaux dogs had an increased lymphoma risk compared with males. Neutered males and spayed females of most breeds were more likely than intact dogs to develop lymphoma, suggesting a possible hormonal influence on the development of lymphoid neoplasia. The authors were not able to determine relative risks of lymphoma subtypes from the available data.

Take-Home Message

The investigators concluded that breed, sex, and neuter status significantly influenced the risk of lymphoid neoplasia development in the examined population of Australian dogs. They stated that the examined factors “need to be considered when evaluating lymphoma risk and can be used to plan studies to identify the underlying etiology of these diseases.”