Epithelioid Sarcoma: Histological Features and Differential Diagnoses

EP: 1.Epithelioid Sarcoma: Overview and Presentation

Now Viewing

EP: 2.Epithelioid Sarcoma: Histological Features and Differential Diagnoses

Summary for Physicians: Histological and Molecular Features of Epithelioid Sarcoma (ES)

Epithelioid sarcoma (ES) typically presents with a painless, slow-growing mass, often in the distal extremities. The classic (distal) subtype is more common in younger patients and generally involves superficial soft tissues, whereas the proximal (large cell) subtype tends to affect older patients and arises in deeper tissues of the pelvis, perineum, or trunk. The proximal subtype is often more aggressive with a worse prognosis.

Histologically, ES is characterized by nodular aggregates of epithelioid and spindle cells with central necrosis, often mimicking granulomatous or epithelial lesions. A key molecular hallmark is the loss of INI1 (SMARCB1) expression, seen in the majority of cases, which aids in diagnosis and may have prognostic and therapeutic implications. The absence of INI1 can help distinguish ES from other morphologically similar tumors and supports the use of targeted therapies currently under investigation. These features play a critical role in accurate diagnosis, prognostication, and guiding treatment decisions.