Transitional cell carcinoma (TCC) is the most common form of urinary tract cancer in dogs and comprises nearly 2% of all canine cancers. The prevalence of TCC has increased 730% over the past 25 years in dogs examined at veterinary teaching hospitals in North America. In dogs, TCC risk is associated with obesity, female sex, familial history of TCC, and urban dwelling, but not to exposure to passive cigarette smoke or household chemicals. Scottish terriers are the breed at highest risk of TCC (18-times higher than mixed breed dogs), although significantly increased risk of TCC is also found in wirehaired fox terriers, West Highland white terriers, and Shetland sheepdogs. This suggests a genetic predisposition to TCC in terriers, especially in Scottish terriers. These findings indicate that veterinarians should recommend performing routine (e.g., twice yearly) cytologic urine examinations in Scottish Terriers and other high risk breeds over 6 years of age.

Two completed case-control studies examined whether use of topical flea and tick products and exposure to lawns or gardens treated with herbicides and insecticides increased the incidence of TCC in Scottish terriers. Owners of genetically predisposed study dogs were recruited through private veterinary practices and the Scottish Terrier Club of America [owners of 87 adult dogs with TCC (cases) and 83 adult dogs with other health-related conditions (controls) completed a written questionnaire in the first study, and owners of 83 adult dogs each of the TCC and control groups completed a questionnaire in the second study].

History of exposure to flea and tick products 1 year prior to diagnosis of TCC was a study requirement for case dogs and a comparable period was surveyed for control dogs. Risk of TCC associated with exposure to flea and tick products was determined by means of univariate and multiple logistic regression analysis.

After adjustment for host factors, Scottish terriers treated with topical spot-on flea and tick products containing fipronil or imidacloprid did not have an increased risk of TCC, compared with Scottish Terriers that had never been exposed to any flea and tick products. The risk of TCC associated with use of older topical flea and tick products such as shampoos, dips, powders, sprays, and collars could not be evaluated because of the low number of owners in the study population that had used such products. Conclusion: Results suggest that use of topical spot-on flea and tick products does not increase the risk of TCC in Scottish terriers.

History of exposure to lawn or garden chemicals 1 year prior to diagnosis of TCC was a study requirement for case dogs and a comparable period was surveyed for control dogs.

The risk of TCC was significantly increased among dogs exposed to lawns or gardens treated with both herbicides and insecticides (odds ratio, 7.19) or with herbicides alone (odds ratio, 3.62). Dogs exposed to lawns or gardens treated with insecticides alone had a small, but not significantly, increased risk of TCC (odds ratio, 1.62) compared with dogs exposed to untreated lawns. The risk of TCC was higher among dogs exposed to phenoxy acid herbicides (odds ratio, 4.42), the most commonly used chemical in agriculture, or nonphenoxy acid herbicides (odds ratio, 3.49), compared with dogs exposed to lawns or gardens that did not receive an herbicide application. Conclusion: Owners of Scottish terriers should decrease their dogs' exposure to lawns or gardens treated with common herbicides, particularly phenoxy herbicides and possibly nonphenoxy herbicides.