Epithelioid Sarcoma: A Review and Update.

Epithelioid sarcoma (EPS) is an ultra-rare malignant mesenchymal neoplasm of uncertain differentiation that comprises two distinct clinicopathological subtypes: classic and proximal. Classic EPS most commonly occurs in the distal upper extremity of adolescents and young adults, whereas proximal-type EPS most often affects the truncal regions of young to middle-aged adults. Both classic and proximal-type EPSs exhibit aggressive clinical behavior, including a higher risk of local recurrence and regional lymph node or distant metastasis. Histologically, classic EPS is characterized by irregular nodules composed of epithelioid and spindled cells, while proximal-type EPS consists of multinodular distributions and sheets of large polygonal cells. EPS has a distinctive immunoprofile with characteristic expression of cytokeratins and epithelial membrane antigen. Loss of nuclear expression of SMARCB1 protein occurs in the vast majority of cases. Moreover, SMARCB1 homozygous deletions have also been observed in both subtypes. Surgery is the mainstay treatment approach for localized EPS. Systemic treatment options for metastatic or unresectable locally advanced disease are very limited. The withdrawal of tazemetostat has created a significant gap in available treatment options. In this review, we provide an overview of the current knowledge on the clinical and radiological features, histopathology, immunohistochemistry, pathogenesis, and management of EPS.