[Epithelioid sarcoma: morphologic variants and differential diagnosis].

Epithelioid sarcoma represents a rare sarcoma with a poor long-term prognosis that arises predominantly on the distal extremities of young adult patients, often mimicking a benign, non-neoplastic condition. Histologically, epithelioid sarcoma is characterized by a multinodular growth with central necrosis, and the neoplasms are composed of relatively uniform epithelioid tumour cells showing a coexpression of vimentin, epithelial membrane antigen and pancytokeratin, and in about half of the cases of CD34. Interestingly, most cases of epithelioid sarcoma show a loss of INI1, whereas the inactivation of the tumour suppressor gene SMARCB1/INI1 is only rarely caused by mutation. The proximal variant of epithelioid sarcoma is composed of confluent sheets of enlarged epithelioid and rhabdoid tumour cells and represents the morphological progression of this entity. The fibroma-like variant of epithelioid sarcoma as well as the angiomatoid and myxoid variants of epithelioid sarcoma are rare morphological variants and need to be considered in the differential diagnosis of other benign and malignant neoplasms.