To evaluate the outcome of patients with oncocytoma of the kidney diagnosed in our center by percutaneous biopsy and treated with watchful waiting.

From January 1998 to April 2004, of 148 solid renal tumors biopsied in our center, 15 were renal oncocytomas. The mean (± standard deviation) follow-up was 30 ± 19.8 months. We report on the outcome of these patients.

The mean age at diagnosis was 57.6 ± 14.4 years, and mean tumor size was 3.49 ± 2.43 cm, corresponding to a mean tumor volume of 62.3 ± 135.4 cm³. During follow-up, 6 of 15 patients needed surgery: two partial and four total nephrectomies. Indications for surgery were initial tumor burden, greater than 0.5 cm/yr tumor growth, and patient’s preference in 1 case, 4 cases, and 1 case, respectively. The patients who received surgical treatment were significantly younger (45.5 ± 11.1 years versus 65.6 ± 10.3 years) and had more bulky tumors at diagnosis (50 ± 30.1 mm versus 27.3 ± 10.5 mm). In 1 patient, a chromophobic renal cell carcinoma was associated with the oncocytoma. All 9 patients who did not receive surgical treatment remained asymptomatic.

The evolution of renal oncocytoma seems to be increase of tumor size with variable velocity. Treatment must be conservative. Initial management might be nonsurgical with close follow-up. Monitoring should not miss the time of conservative surgery. Initial tumor volume or fast tumor growth are indications for surgery. Partial nephrectomy, if the tumor size and localization are reasonable, is currently the technique of choice.