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 p rostate carcinoma. The purpose of this study was to further characterize th e clinical and pathologic features of spontaneous canine prostate carcinoma . METHODS. A multiinstitutional, retrospective study was conducted using 76 d ogs with prostate carcinoma that underwent postmortem evaluation. For each case, clinical and pathologic data were tabulated and hematoxylin/eosin-sta ined tissue sections from the primary tumor and metastatic lesions were eva luated. 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 p resence of skeletal metastases. RESULTS. The vast majority of canine prosta te carcinomas affected elderly sexually intact dogs or dogs that underwent surgical castration after sexual maturity. Adenocarcinoma was the most freq uent histologic type, although more than half of canine prostate carcinomas exhibited intratumoral heterogeneity. In many eases, primary tumors showed mixed morphology, characterized by two or more types of differentiation. D uration 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 me tastases were present in 22% of cases, and the predominantly axial skeletal distribution of these lesions was similar to that reported in men with pro state carcinoma. Young dogs were at highest risk for development of skeleta l metastases. CONCLUSIONS. This study provides a more complete characterization of sponta neous prostate carcinoma of dogs in terms of morphologic heterogeneity, ske letal metastases, and the influence of testicular hormones. Prostate carcin oma in pet dogs provides an immunocompetent, autochthonous tumor system tha t mimics certain aspects of human prostate cancer. This spontaneous model m ay contribute to our understanding of the factors that regulate carcinogene sis within the aged prostate, and to the development of chemoprevention str ategies or bone-targeted therapies. Prostate 45:173-183, 2000. (C) 2000 Wil ey-Liss, Inc.