Thyroid cancer in dogs: an update based on 638 cases (1995-2005).

The goal of this study was to update the descriptive statistics of thyroid cancer by using data from multiple institutions collected through the Veterinary Medical Database (VMDB). Information was collected and reported from cases of canine thyroid cancer submitted to the VMDB between January 1, 1995 and December 31, 2005. Odds ratio (OR) analysis was performed on breeds that had > or =3% of the total number of dogs with thyroid cancer; ORs for each age category were also determined. Thyroid cancer represented 1.1% of all neoplasms during the time period of interest. Golden retrievers, beagles, and Siberian huskies all had significantly increased ORs for developing thyroid cancer. No sex predisposition was evident, but dogs between 10 and 15 years of age had a significantly increased chance of developing thyroid disease. Carcinomas and adenocarcinomas represented 90% of thyroid cancers, while adenomas represented 9.3%. Thyroid carcinoma and adenocarcinoma continue to be uncommon in our canine population. Older dogs are still more commonly affected, and this study is in agreement with previous studies that golden retrievers and beagles are overrepresented. A new finding is that Siberian huskies are also overrepresented. Carcinomas represent a much higher proportion of thyroid cancers than previously reported, and adenomas are likely incidental findings on necropsy. Thyroid cancer should be high on the list of differentials for a neck mass in older, large-breed dogs, as they make up 1.1% of the cancer cases reported. The overwhelming majority of thyroid cancers are carcinomas, and they are most common in golden retrievers, beagles, and Siberian huskies.