Incidence, histopathologic and electron microscopic features of spontaneous nephroblastomas in rats

Primary renal neoplasms in the rats are uncommon. Nephroblastoma is the only renal embryonal tumor of the rat; all other tumors are reported in older rats. The occurrence of spontaneous nephroblastoma in rats has been reported. However, metastasis from the nephroblastoma in rat is extremely rare. Data from 2669 Sprague-Dawley control rats and 1060 Fischer-344 rats were reviewed and evaluated to determine the incidence and pathology of nephroblastoma. This tumor was observed in three Sprague-Dawley rats. Metastasis was observed in the lungs and renal lymph nodes in two different rats. No case of nephroblastoma was observed in Fischer-344 rats. Detailed histopathological and electron microscopic features of these neoplasms are described and discussed.