Epithelioid sarcoma was first described
by Enzinger (1970 Epithelioid sarcoma. A
sarcoma simulating a granuloma or a carcinoma.Cancer 26:1029-1041).
This rare malignant tumour occurs in adolescents and young adults.
Epithelioid sarcoma 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.
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.
HISTOLOGICAL FEATURES:
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USUAL EPITHELIOID SARCOMA :
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- 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:
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- 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.
IMMUNOHISTOCHEMISTRY
The following markers are positive:
Keratin (K8 is positive in almost all cases, K19 is positive in some
cases), EMA, Vimentin, CD34 (patchy membrane positivity), muscle specific
actin (diffuse staining).
Coexpression of keratin, vimentin and EMA is characteristic of epithelioid
sarcoma.
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