Abstract
Sarcomatoid component can occur in all histological subtypes of renal cell carcinoma but most commonly accompanies chromophobe renal cell carcinoma. The majority of the sarcomatoid components consist of malignant fibrous histiocytoma, fibrosarcoma or undifferentiated sarcoma areas. Heterologous differentiation in the form of osteosarcoma or rhabdomyosarcoma is very rarely encountered. We report a very rare case of a chromophobe renal cell carcinoma with osteosarcomatous differentiation that presented as a retroperitoneal mass. Renal cell carcinoma with sarcomatoid change should be always kept in mind when a retroperitoneal mass with sarcomatoid differentiation is encountered.
Highlights
Chromophobe renal cell carcinomas (CRCC) are a rare renal cell carcinoma (RCC) variant that make up approximately 6% of all RCC cases (1)
We present a case with a retroperitoneal mass that was first thought to be a malignant mesenchymal tumor on intraoperative frozen section but was diagnosed as sarcomatoid CRCC with osteosarcomatous differentiation on paraffin sections
CRCC cases have a typical appearance consisting of polygonal cells with a perinuclear clear halo, pale or eosinophilic cytoplasm and prominent cytoplasmic borders (1,2)
Summary
Chromophobe renal cell carcinomas (CRCC) are a rare renal cell carcinoma (RCC) variant that make up approximately 6% of all RCC cases (1). CRCC have a better prognosis than other RCC subtypes in general (1,2). Sarcomatoid differentiation of CRCC generally indicates a worse prognosis as with all RCC cases (3-7). Sarcomatoid component is found in approximately 8% of all CRCC cases (2,3). The sarcoma component of RCC generally consists of sarcoma areas such as malignant fibrous histiocytoma or fibrosarcoma (8). There may very rarely be heterologous differentiation in the form of osteosarcoma or rhabdomyosarcoma. We present a case with a retroperitoneal mass that was first thought to be a malignant mesenchymal tumor on intraoperative frozen section but was diagnosed as sarcomatoid CRCC with osteosarcomatous differentiation on paraffin sections
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