Epithelioid Sarcoma

Definition

Keratin positive soft tissue tumor composed of large epithelioid cells almost always involving distal extremities (see also proximal type epithelioid sarcoma)

95% keratin positive
- CD34 50%
Almost always involves distal extremities of young adults and children
Poorly circumscribed, often multinodular
- Separate and fused nodules and sheets of cells
Frequent central necrosis
- May appear histologically as necrotic granulomas
Brightly eosinophilic collagen in and around nodules
Medium to large epithelioid and spindled cells
- Rarely predominantly spindled
- Abundant brightly eosinophilic cytoplasm
- Frequently with sharp cell borders
- Nuclei may be eccentric
- Moderate nuclear pleomorphism
- Mitotic figures infrequent to numerous
Occasional features
- Perineural invasion
- Vascular invasion
- Myxoid areas or extensive hyalinization
- Calcification or ossification
- Hemorrhage
- Cyst formation
- Small cell pattern with scant cytoplasm
Fibroma-like variant
- Pure spindled cells
Other than the name, classical type epithelioid sarcoma shares only the distinctive immunophenotype of proximal type epithelioid sarcoma.

Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342