Clear cell sarcoma of the kidney misdiagnosed as mesoblastic nephroma: a case report and review of the literature.

Clear cell sarcoma of the kidney (CCSK) is a rare renal neoplasm of paediatrics, making up about 3% of all renal tumours in paediatrics, with a high tendency for developing bone metastasis. A seven year-old boy was referred to our clinic with two firm, large masses over the manubrium of the sternum and right frontal area, which pathologically were confirmed as a metastatic CCSK. The patient had a history of a renal mass three years earlier, for which radical nephrectomy had been performed, and histopathologic diagnosis was compatible with mesoblastic nephroma. Thus, no further investigation and therapy had been applied for the patient. CCSK is a rare but malignant and aggressive paediatric renal tumour, with a high tendency for developing distant bone metastases, leading to its poor prognosis. CCSK could be misdiagnosed as several other renal tumours such as mesoblastic nephroma, and thus CCSK should be taken carefully into consideration in the diagnosis of renal tumours.