Large clear cell sarcoma of the kidney mistaken as Wilms' tumor

Clear cell sarcoma of the kidney (CCSK) is a rare tumor. It has a wide histologic spectrum and often mimics other pediatric renal tumors, resulting in considerable diagnostic difficulty. We report the case of a two-year-old who presented with a large (14 cm) abdominal mass. Prior to neoadjuvant chemotherapy, a biopsy was performed, which revealed Wilms' tumor. The final pathology diagnosis at the time of resection revealed CCSK.