Renal oncocytoma with synchronous contralateral renal cell carcinoma: A report of two cases

We report two cases of renal oncocytoma with contralateral renal cell carcinoma. [Case 1] A 72-year-old man was admitted with a 17 mm right renal mass incidentally found by computed tomography. Under the diagnosis of right renal cell carcinoma, we performed radical right nephrectomy. Pathological diagnosis was renal cell carcinoma, four months later, another renal mass was found in the left kidney by computed tomography, and this mass had a diameter of 13 mm. We could not rule out the possibility of contralateral renal cell carcinoma. We performed left partial nephrectomy. Pathological diagnosis was oncocytoma. [Case 2] The patient was 61-year-old woman, who had been on hemodyalysis for 27 years. CT revealed bilateral renal masses, which had a diameter of 30 mm (right kidney), and 20 mm (left kidney). We diagnosed the case as bilateral renal cell carcinoma. Firstly, we performed laparoscopic left nephrectomy. Then, laparoscopic right nephrectomy was performed two months later. Pathological diagnosis was left papillary renal cell carcinoma and right oncocytoma. To our knowledge, these are the fourth and fifth cases of renal oncocytoma with synchronous contralateral renal cell carcinoma to be reported in Japan.