Confirming Epithelioid Sarcoma: Diagnostic Approach, Imaging, and Molecular Markers

EP: 1.Epithelioid Sarcoma: Overview and Presentation

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

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EP: 3.Confirming Epithelioid Sarcoma: Diagnostic Approach, Imaging, and Molecular Markers

Summary for Physicians: Diagnostic Approach to Suspected ES

When evaluating a patient with suspected ES, a thorough diagnostic workup is essential to confirm the diagnosis and assess disease extent. Initial evaluation typically includes MRI of the primary site to define local anatomy and soft tissue involvement, along with CT imaging of the chest to evaluate for pulmonary metastases. PET/CT may be considered in selected cases for comprehensive staging.

Histopathologic evaluation with core needle biopsy is critical. Immunohistochemistry is used to assess for loss of INI1 (SMARCB1), a key diagnostic marker that supports ES diagnosis and helps distinguish it from histologic mimics. Molecular testing may also be used to rule out other entities or identify targetable alterations.

The presence of INI1 loss has both diagnostic and potential therapeutic implications, as it may inform eligibility for specific clinical trials or guide consideration of emerging targeted therapies. Multidisciplinary evaluation is key to establishing diagnosis, determining resectability, and developing an appropriate treatment strategy.