Vet Pathol 29250-253 (1992) The Histologic, Ultrastructural, and Immunohistochemical Features of a

Nephroblastoma is a rare tumor in dogs. There is no ap-parent breed or sex predilection; most affected dogs are less than 1 year old, and most tumors are malignant.4 Nephro-blastomas are generally thought to be mixed renal tumors arising from metanephric blastema (nephrogenic mesen-~ h y m e). ~ , ~. ~ , ~ Morphologic similarities between nephroblas-toma and the developmental stages of embryonic kidneys have resulted in strong support7 for speculations that the tumor results from malignant transformation that occurs during normal nephrogenesis * or results from neoplastic transformation of rests of tissue with embryonic potentiali-ties that persist in postnatal kidneys.2 We report a blastema-predominant histologic subtype of nephroblastoma in a poly-cythemic dog and emphasize the histogenic similarity of that tumor to Wilms ’ tumor in children