Oncocytomas of the kidney

Fourteen cases of renal oncocytomas are presented. By definition these lesions are composed entirely of pink eosinophilic cells with abundant granular cytoplasm. No evidence of mitotic activity or necrosis was seen in any of the cases, although focal areas of nuclear pleomorphism were identified in two cases. Clinically the patients have remained asymptomatic and without evidence of metastatic or recurrent disease in a follow-up that ranges from 1-14 years. The clinical behavior of these tumors favors the benign nature of the lesion regardless of the tumor size.