Bilateral gonadoblastomas in a dog with mixed gonadal dysgenesis.

Gonadoblastomas are rare mixed germ cell neoplasms, which are frequently diagnosed in testes excised for other reasons. In human patients these tumours are usually associated with undescended testes or dysgenetic gonads. This report describes a 10-year-old male dog with mixed gonadal dysgenesis ("streak testis" on the right side and testis on the left side) and bilateral gonadoblastomas. Immunohistochemical analysis revealed an atypical and mitotically active germ cell population which co-expressed placental alkaline phosphatase and c-kit oncogene, admixed with inhibin- and S-100 protein-positive sex cord cells. The findings were generally consistent with previous reports of the dual population of neoplastic cells in gonadoblastomas affecting human patients, and closely resembled the findings in the only other case reported in dogs. Moreover, the findings further support the proposal that gonadoblastomas should be considered a special form of in-situ germ cell neoplasia.