Pathology of Epithelioid Sarcoma 

Dr Sampurna Roy MD                        2022

This rare malignant  tumour occurs in adolescents and young adults.

ES is usually located on the distal extremities (hands, fingers and forearm).

This tumour rarely occurs on the pelvis, perineum and vulva.

The tumour spreads along fascial and neurovascular structures with formation of satellite nodules.

Multiple recurrences are known to occur in this tumour.

Metastasis to the scalp, lymphnode and lungs occur frequently.

Adequate treatment requires early radical excision or amputation if the tumour is located in the fingers or toes.

Regional lymphnode dissection should be included as lymphnode metastasis is common in epithelioid sarcoma.

Surgical excision is combined with radiotherapy.

Loss of expression of INI1 is frequent in the conventional and large cell subtypes of ES and can be used as a diagnostic marker, but it has no prognostic impact.

Gross features: 

The superficial lesion presents as a slow growing, firm tan white nodules or plaques, 0.5 - 5cm in diameter.

These lesions are often ulcerated.

The deeper lesions are attached to the tendon or fascia.

These are larger in size and present as less well defined mutinodular masses or as an area of induration, usually 3-6 cm in diameter.    

Usual Epithelioid Sarcoma 

- Distinct nodular appearance

- Central necrosis of the tumour nodule.

- Fusion of several necrotizing nodules with formation of 'geographic lesion'.

- Tumour composed of oval or polygonal cells with eosinophilic cytoplasm.

There is gradual transition into plump spindle cells.

- Scattered mitotic figures.

- Minimal nuclear pleomorphism.

- Conspicuous inflammatory cell infiltrate composed of lymphocytes and histiocytes surrounding the tumour nodule.

- Focal calcification and osseous metaplasia.

- Intercellular dense hyalinized collagen. 

- In some cases cytoplasmic vacuolation may be present simulating lumen formation. These are intracellular lipid droplets.

- The tumour may grow along neurovascular bundles and invest large vessels and nerves.

 Proximal -Type Epithelioid Sarcoma

- Sheets of large epithelioid like cells with  rhabdoid inclusions.

- Central necrosis is absent

- These are aggressive tumours and the differential diagnosis includes undifferentiated carcinoma and  extrarenal rhabdoid tumour.

Both classic and proximal-types are associated with the loss of SMARCB1/INI1 protein expression.

Immunohistochemistry:

The following markers are positive:

Cytokeratin (K8 is positive in almost all cases, K19 is positive in some cases), EMA, CD34 (patchy membrane positivity), muscle specific actin (diffuse staining).

Differential diagnosis: 

I Superficially located small tumour: 

(Tumour cells in ES are larger and more eosinophilic. Diagnosis is confirmed by immunohistochemistry)

- Necrobiotic  process - Granuloma annulare, Necrobiosis lipoidica, Rheumatic nodule

- Nodular fasciitis

- Dermatofibroma

II Larger and deeper lesions:

-  Epithelioid vascular malignancy

(Epithelioid angiosarcoma;  Epithelioid hemangioendothelioma)

-Synovial sarcoma 

- Melanoma 

- Squamous Cell Carcinoma

(No dyskeratosis or any involvement of the epidermis in epithelioid sarcoma).

Epithelioid Sarcoma: Diagnostic Features and Genetics.

Proximal-type epithelioid sarcoma-unusual presentation: unilateral vulvar mass.

Epithelioid sarcoma resembling benign fibrous histiocytoma.

Consistent SMARCB1 homozygous deletions in epithelioid sarcoma and in a subset of myoepithelial carcinomas can be reliably detected by FISH in archival material.

Proximal-Type Epithelioid Sarcoma: Report of Two Cases in the Perineum: Differential Diagnosis and Review of Soft Tissue Tumors With Epithelioid and/or Rhabdoid Features.

Cytokeratin 7 and 20 expression in Epithelioid sarcoma. 

Epithelioid sarcoma:  An immunohistochemical analysis evaluating the utility of cytokeratin 5/6 in distinguishing superficial epithelioid sarcoma from spindled squamous cell carcinoma. 

Proximal-Type Epithelioid Sarcoma. A Clinicopathologic Study of 20 cases.

Epithelioid sarcoma:  the clinicopathological complexities of this rare soft tissue sarcoma. 

Epithelioid sarcoma: an immunohistochemical analysis of 112 classical and variant cases and a discussion of  the differential diagnosis.