This university clinic retrospective study (1993-1998) of 15,363 male dogs investigated the frequency of prostate carcinoma (PCA) among 225 dogs with prostate disease and included another 206 dogs referred on the basis of cytologic biopsy examination. Thus, the total number of dogs studied was 431, with the remainder as population control. In dogs with prostate disorders, benign prostatic hyperplasia (BPH) was diagnosed in 246 (57%), prostatitis in 83 (19.3%), and PCA in 56 (13%). Only 6.7% of the dogs with nonmalignant prostate disorders were castrated, and 46% (26) of the 56 dogs with PCA had been castrated. Dogs with PCA were significantly older (mean, 9.9 years) than dogs with other prostate diseases (mean, 8.4 years). The interval between castration and onset of prostate problems was highly variable (range, 1 to 10 years), and age at PCA diagnosis did not differ significantly between castrated and intact dogs. This suggests that castration does not initiate development of PCA, even though it does seems to favor tumor progression.

COMMENTARY: This article supports previous studies showing BPH as the most common prostate disease in dogs; that prostate carcinoma is relatively rare; and that the prevalence of prostate carcinoma is higher in castrated dogs than in intact dogs. The age of castration had no effect on the age at which the tumor was diagnosed. Because prostate carcinoma is so rare in both intact and neutered dogs, this should not be a deterrent to castration. Prostate carcinoma is seen only in dogs older than 6 years. When prostate disease is diagnosed in castrated dogs, the probability of cancer is very high. 

Canine prostate carcinoma: epidemiological evidence of an increased risk in castrated dogs. Teske E, Naan EC, van Dijk EM, Van Garderen E, Schalken JA. Molec Cell Endocrinol 197:251-255, 2002.