Primary Sclerosing Epithelioid Fibrosarcoma of the Kidney: A Case Report and Review of the Literature

Sclerosing epithelioid fibrosarcoma (SEF) is a rare variant of fibrosarcoma. We report one case of primary kidney SEF occurring in a 38-year-old man. Microscopically, epithelioid neoplastic cells are mainly arranged in cords and nests embedded in the dense sclerosing stroma. Diffuse immunohistochemical staining for MUC4 in neoplastic cells and the presence of the EWSR1 gene split by fluorescence in situ hybridization (FISH) analysis confirmed the histological diagnosis. Primary kidney SEF is extremely rare, the differential diagnosis strategy broadly includes a series of tumors with epithelioid morphology and sclerosing matrix, mainly including sclerosing variants of clear cell sarcoma of the kidney (CCSK), renal synovial sarcoma (SS), renal solitary fibrous tumor (SFT), metanephric stromal tumor (MST), sclerosing perivascular epithelioid cell tumor (PEComa), and carcinomas, and immunohistochemical expression of MUC4 and evidence of the EWSR1 gene split are helpful in making a definite diagnosis.