Proximal Type Epithelioid Sarcoma

Definition

Keratin positive soft tissue tumor composed of large epithelioid cells occurring in a proximal location (see also classical type epithelioid sarcoma)

95% keratin positive
- CD34 50%
Most often involves pelvis, perineum and proximal extremities
- May involve head, neck and trunk
- May involve penis and vulva
Median age 35-40 years
Poorly circumscribed, may be multinodular
- Separate and fused nodules and sheets of cells
- Granuloma-like nodularity less common than in classical type epithelioid sarcoma
Medium to large epithelioid and spindled cells often with rhabdoid appearance
- Rarely predominantly spindled
- Abundant brightly eosinophilic to amphophilic cytoplasm
- Frequently with sharp cell borders
- Often has eccentric nuclei
- 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
Variant patterns

Fibroma-like
- Pure spindled cells
Angiomatoid
- Large vascular-like spaces formed by discohesion
- May be blood filled
Large cell or rhabdoid
- Largely coincides with proximal type

Other than the name, proximal type epithelioid sarcoma shares only the distinctive keratin positive, CD34 frequently positive phenotype of classical type epithelioid sarcoma.

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