Renal oncocytoma--bilateral, multifocal.

One hundred thirteen cases of "grade I renal oncocytoma" are reported from several centers. All centers report absence of associated metastatic disease. In the present review of 219 radical nephrectomy specimens, 11 renal oncocytomas were identified, an incidence of 5 per cent. No diagnostic angiographic features could be identified. Multifocal potential is exemplified by study of a bilateral case and 2 cases of 2 independent oncocytomas in the same kidney. The fine histologic criteria distinguishing oncocytoma from malignant renal tumors suggest that the oncocytomas may have the potential of malignant degeneration. The possible "premalignant classification" of oncocytomas and the lack of dependable diagnostic features radiographically force the management to be the same as for Stage I renal carcinoma. The prognostic information available after histologic definition of renal oncocytoma is valuable.