Proximal-type epithelioid sarcoma

Abstract

Proximal-type epithelioid sarcoma (PES) is a rare variant of epithelioid sarcoma (ES) presenting in either a proximal extremity or axial location. Compared to the classic type of ES, the proximal variant demonstrates more aggressive behavior. The classic and proximal epithelioid variants of ES are characterized by co-expression of cytokeratin and vimentin. Loss of integrase interactor-1 (INI1) staining is a recently characterized feature that narrows the differential diagnosis.