Clinical and pathologic aspects of spontaneous canine prostate carcinoma: A retrospective analysis of 76 cases

BACKGROUND Pet dogs and men share a vulnerability for the development of prostate carcinoma. The purpose of this study was to further characterize the clinical and pathologic features of spontaneous canine prostate carcinoma. METHODS A multiinstitutional, retrospective study was conducted using 76 dogs with prostate carcinoma that underwent postmortem evaluation. For each case, clinical and pathologic data were tabulated and hematoxylin/eosin-stained tissue sections from the primary tumor and metastatic lesions were evaluated. Prostatic carcinomas were subclassified based upon the presence of glandular, urothelial, squamoid, or sarcomatoid differentiation. We focused our analysis on dogs that differed with respect to morphologic features of the primary tumor, lifetime duration of testicular hormone exposure, and presence of skeletal metastases. RESULTS The vast majority of canine prostate carcinomas affected elderly sexually intact dogs or dogs that underwent surgical castration after sexual maturity. Adenocarcinoma was the most frequent histologic type, although more than half of canine prostate carcinomas exhibited intratumoral heterogeneity. In many cases, primary tumors showed mixed morphology, characterized by two or more types of differentiation. Duration of testicular hormone exposure was significantly different between dogs with adenocarcinoma and dogs with mixed morphology tumor, but did not appear to influence the frequency or pattern of metastases. Overall, gross metastases were present in 80% of dogs with prostate carcinoma. Skeletal metastases were present in 22% of cases, and the predominantly axial skeletal distribution of these lesions was similar to that reported in men with prostate carcinoma. Young dogs were at highest risk for development of skeletal metastases. CONCLUSIONS This study provides a more complete characterization of spontaneous prostate carcinoma of dogs in terms of morphologic heterogeneity, skeletal metastases, and the influence of testicular hormones. Prostate carcinoma in pet dogs provides an immunocompetent, autochthonous tumor system that mimics certain aspects of human prostate cancer. This spontaneous model may contribute to our understanding of the factors that regulate carcinogenesis within the aged prostate, and to the development of chemoprevention strategies or bone-targeted therapies. Prostate 45:173–183, 2000. © 2000 Wiley-Liss, Inc.