Renal oncocytoma.

Review of the Mayo Clinic tissue registry for the years 1950 to 1979 identified 90 cases of pure, well differentiated eosinophilic granular cell renal tumors. The clinical, laboratory, pathologic and survival features of these patients were analyzed. Fifty-nine per cent of these tumors were discovered incidentally during an examination for other problems and 91 per cent were confined within the renal capsule, with no evidence of local invasion. Sixty-two patients had grade 1 and 28 had graded 2 tumors. None of the patients with grade 1 tumors developed metastases. Four of the patients with grade 2 tumors died of metastatic disease. Survival curves show no difference in survival between patients with these renal tumors, and an age and sex matched cohort. If the term renal oncocytoma is used to signify a very well differentiated (grade 1) eosinophilic granular cell renal parenchymal tumor then this study demonstrates that renal oncocytomas are non-aggressive tumors with a highly favorable prognosis.