Mediastinal parathyroid adenocarcinoma in a dog.

A tumor in the anterior mediastinum was found in an adult male German Shorthaired Pointer. The dog presented with hypercalcemia that varied with the removal and recurrence of the tumor. The neoplasm was characterized by an encapsulated multilobed grey-white soft mass with stroma, and the recurrent tumor infiltrated veins and the heart. The tumor consisted of groups of clear cells with well outlined cytoplasmic boundaries separated by thin vascular stroma. These cells had few organelles, scattered clumps of glycogen, clear cytosol and prominent infolding and interdigitating plasma membranes and desmosomes. The clinical, light and electron microscopic features were consistent with a functional neoplasm of parathyroid tissue origin.