Epithelioid sarcoma is a rare, malignant soft-tissue neoplasm occurring on the distal extremities of young adults.
First described in 1970, epithelioid sarcoma accounts for less than 1% of soft tissue sarcomas. It arises from multipotential mesenchymal cells able to express both epithelial and mesenchymal immunophenotype, and typically shows a slow-growing pattern.
Epithelioid sarcoma occurs more frequently in the upper limbs, usually involving the extremities (hand and wrist) of young to middle-aged male adults.
This "classic" form of epithelioid sarcoma is composed by cells varying from spindle to round and epithelioid, with necrotic areas. A recently reported "proximal"-type variant is characterized by higher aggressiveness and preferential location in proximal-axial and deep regions.
In a recent study, frequent deletions of INI1 gene have been detected in the proximal-type variant, by both real-time quantitative PCR analysis and immunohistochemistry.
Interestingly, the recognition of INI1 deletion in this extradural clival tumor with rhabdoid features reminds one of the atypical teratoid/rhabdoid tumor (AT/RT), a high malignant pediatric brain neoplasm, typically containing rhabdoid cells and divergent differentiation along epithelial, mesenchymal, neuronal or glial pathways.
AT/RTs are associated with inactivation of INI1 gene. Moreover, very similar morphological and immunohistochemical findings (including INI1 deletion) have been reported in both malignant renal and extra-renal rhabdoid tumors, thus making the differential diagnosis difficult and problematic.
Despite their slow growth, epithelioid sarcomas tend to spread locally, infiltrating regional lymph nodes and can present as multinodular and/or metastatic disease. The reported recurrence rate is as high as 70%. Treatment is primarily by wide local excision, followed by adjuvant radiotherapy; however, even in cases of primary amputation of an affected limb, no survival advantage has been observed.
The final diagnosis required histologic examination which showed epithelioid neoplastic cells, with rounded nuclei and abundant eosinophilic cytoplasm, numerous mitoses, a high proliferative index and areas of necrosis. Immunohistochemistry, demonstrating a positive stain for vimentin, cytokeratins, and EMA, and the failure of BAF-47 antibody to stain neoplastic nuclei (suggesting INI1 deletion), were in favor of epithelioid sarcoma.
Synopsis
proliferation of rounded to plump, spindle-shaped cells with abundant eosinophilic cytoplasm around areas of necrosis
Variants
proximal-type epithelioid sarcoma (15078349)
- pelvic and perineal areas
- young to middle-aged adults
- proliferation of epithelioid-like cells with rhabdoid features in the absence of a granuloma-like pattern
- immunohistochemistry: vimentin+, cytokeratin+, epithelial membrane antigen+, CD34+
- differential diagnosis: tumors with rhabdoid features, extrarenal malignant rhabdoid tumor
Subtypes
proximal-type epithelioid sarcoma
classic epithelioid sarcoma
Differential diagnosis
granulomatous inflammation
epithelioid granulomas (tuberculoid granulomas)
hemangioendotheliomas (12502927)
References
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Billings SD, Folpe AL, Weiss SW. Epithelioid sarcoma-like hemangioendothelioma. Am J Surg Pathol. 2003 Jan;27(1):48-57. PMID: 12502927
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