Findings from the Swiss Canine Cancer Registry, 1955-2008

An analysis of cancer in dogs from a large European cancer registry has recently been published in the Journal of Comparative Pathology.

The Swiss Canine Cancer Registry includes records of pathological examinations of 121,693 dogs from 1955 to 2008. Examinations were conducted at 3 Swiss diagnostic laboratories. Samples were collected either antemortem (by cytology or biopsy) or postmortem. A total of 67,943 tumors were confirmed in 63,214 dogs.

Tumor types

Adenomas/adenocarcinomas were the most common tumors (18.09%) and were found most often in the mammary gland and gastrointestinal tract. The frequency of adenoma/adenocarcinoma diagnosis decreased from 40.6% in 1980 to 12.3% in 2008. The authors suggest that because 60% of these tumors were identified in sexual organs, this drop could be related to the decrease in the percentage of intact dogs examined during that time (from 92.8% of all dogs examined in 1980 to 55.6% in 2008). Advances in diagnostic techniques over the decades could also have affected the results.

Other relatively common tumor types were mast cell tumors (6.5%), which were mostly found in the skin; lymphoma (4.35%), found most often in lymph nodes; melanocytic tumors (3.63%), nearly all of which were in the skin; and fibroma/fibrosarcomas (3.4%), usually found in soft tissues or skin. Hemangiomas/hemangiosarcomas, squamous cell carcinomas, and osteomas/osteosarcomas each comprised less than 3% of the total number of tumors.

Breed associations

Breed designations include both mixed-breed and purebred dogs. Mixed-breed dogs were assigned to the first breed named in the diagnostic record (eg, a boxer-shepherd cross was classified as a boxer and a shepherd-boxer cross was classified as a shepherd), presuming that this would best reflect each dog’s predominant phenotype. Dogs with no specific breed named were classified as crossbred dogs.

The overall cancer risk was not significantly different between crossbred dogs and those assigned to a breed category. Other studies have shown a higher incidence of neoplasia in purebred dogs than in mixed breeds. The authors attribute this discrepancy to different data collection or breed allocation methods. They suggest that genetic testing would remove uncertainty in future studies.

Selected breed-specific results include the following:

• Boxers had the highest overall risk for tumor development compared with crossbred dogs (the standard to which specific breeds were compared). Boxers had an especially high risk for mast cell tumor—nearly 5 times that of crossbreeds—and were also at nearly twice the risk for hemangioma/hemangiosarcoma.
• Schnauzers were 7 times as likely as crossbreeds to have squamous cell carcinoma and twice as likely to have melanocytic tumors.
• Great Danes and Rottweilers were at notably high risk of osteoma/osteosarcoma. Great Danes were nearly twice as likely and Rottweilers were more than 3 times as likely as crossbreeds to have these tumors.
• Shepherds were almost twice as likely as crossbreeds to have hemangioma or hemangiosarcoma.
• Compared with crossbred dogs, breeds with a higher overall risk for neoplasia were (in descending order) boxers, cocker spaniels, poodles, Swiss mountain dogs, dachshunds, setters, schnauzers, and retrievers.
• Breeds with a lower overall risk for neoplasia were great Danes, bulldogs, West Highland white terriers, Parson Jack Russell terriers, Rottweilers, Dobermans, collies, shepherds, and Yorkshire terriers.
• Small dogs were 3 times as likely as large dogs to have mammary tumors and about 1.5 times as likely to have endocrine gland tumors. The authors speculate that the tendency of small dogs to have shorter sexual cycles (and therefore higher exposure to sex hormones) could explain their increased risk of mammary tumors.

Age associations

Overall tumor risk increased with age for some tumor types, such as adenoma/adenocarcinoma, melanocytic tumors, and squamous cell carcinoma. In contrast, the frequency of lymphoma peaked at 6 years of age and then declined.

Neutering associations

Compared with intact dogs, neutered dogs of both sexes had a higher risk of tumors in locations other than the genitalia. Neutered dogs had a higher risk of lymphoma and mast cell tumor (both sexes), adenoma/adenocarcinoma and osteoma/osteosarcoma (males), and hemangioma/hemangiosarcoma and melanocytic tumors (females). Results related to neutering status depended partly on the time of sample collection; tumor incidence in postmortem samples was higher for neutered dogs than for intact dogs. The authors note that this could represent a sampling bias.

“The reproducibility of cancer epidemiological studies is greatly affected by the absence of international standards for veterinary cancer registries,” write the authors. They recommend the development of guidelines to standardize data collection in cancer registries. They also suggest further investigation to verify their results, especially those that were new or different from those of previous studies.

The study received financial support from the University of Zurich and Dr R. Dähler.