Clear Cell Renal Cell Carcinoma With Extensive Osseous Metaplasia: Report of a Rare Case.

A 48-year-old Chinese woman presenting with continuing dull pain in the right lower back and abdomen was found to have a tumor with extensive osseous metaplasia in the upper-middle pole of the right kidney. The excised neoplasm specimen revealed a 29 × 26 mm hard tumor with dense ossification. Histopathological examination of the tumor showed that it contained lamellar bone forming trabeculae intermingled and spherical or polygonal epithelial cells that contained slightly irregular nuclei with small nucleoli and abundant pink to clear cytoplasm. Clear cell renal cell carcinoma with extensive osseous metaplasia is a very rare occurrence.