[Two cases of renal cell carcinoma accompanied with ossification]

We report two cases of renal cell carcinoma accompanied with ossification. Case 1: A 40-year-old male visited a physician with the complaint of epigastric pain. Examination of the stomach revealed compression of the greater curvature. Abdominal radiography and CT scan revealed a left renal mass with calcification, which was a hypovascular tumor on angiography. A transperitoneal left nephrectomy was performed. The resected kidney was 700g in weight and the tumor, which was 12 x 10 x 10 cm in size and located in the upper pole of the kidney, was enveloped with a hard capsule and was extensively necrotized. Histopathological diagnosis was renal cell carcinoma (papillary type, mixed subtype). Case 2: A 69-year-old female was occasionally pointed out to have a left renal mass in ultrasonic examination. It was accompanied with calcification in CT scan and a hypervascular tumor in angiography. A transperitoneal left nephrectomy was performed. The resected kidney was 320 g in weight and the tumor located in the lower pole of the kidney, was 6 x 6 x 6 cm in size and necrotized. Histopathological diagnosis was renal cell carcinoma (alveolar type, clear cell subtype). Microscopically in both cases, ossified tissue existed among the fibrous tissue in the necrotized lesion of the tumor, but not near the cancer cells and, it was accompanied by calcification. During the ossification process, the connective tissue proliferates after the necrosis of the tumor, and metaplasia occurred from its juvenile plastic cells to osteoblastic cells.