Body conformation, diet, and risk of breast cancer in pet dogs: a case-control study.

Canine and human breast cancer share several important clinical and histologic features. A case-control study of nutritional factors and canine breast cancer was conducted at the Veterinary Hospital of the University of Pennsylvania in 1984-1987 by interviewing owners of 150 pet dogs diagnosed with breast cancer, owners of 147 cancer control dogs, and owners of 131 noncancer control dogs. The risk of breast cancer was significantly reduced in dogs spayed at or before 2.5 years of age. Neither a high-fat diet nor obesity 1 year before diagnosis increased the risk of breast cancer according to multiple logistic regression analysis. However, the risk of breast cancer among spayed dogs was significantly reduced in dogs that had been thin at 9-12 months of age (odds ratio (OR) = 0.04 (95% confidence interval (CI) 0.004-0.4) and OR = 0.04 (95% CI 0.004-0.5) for cases vs. cancer controls and cases vs. noncancer controls, respectively, after adjustment for age at spay). Among intact dogs, the risk associated with being thin at 9-12 months of age was reduced, but not significantly so (OR = 0.60 (95% CI 0.2-1.9) and OR = 0.51 (95% CI 0.2-1.4) for the two comparisons, respectively). Results of this study suggest that nutritional factors operating early in life may be of etiologic importance in canine breast cancer.