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Presented by Dr. P. Argani and prepared by Dr. A. McCuiston.
Case 3: This is a 34 year old male with an arm mass.
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1. Question
This is a 34 year old male with an arm mass.
AE1/AE3
CD34
INI-1
Correct
Answer: Epithelioid sarcoma
Histology: This is a multinodular proliferation of epithelioid cells within the dermis and subcutaneous tissue. Focally, the nodules form tight rounded clusters and are associated with central necrosis, simulating a necrotizing granuloma. However, the lesion does demonstrate greater cytologic atypia than would be expected for benign histiocytes, including rhabdoid cytology in several foci. Moreover, mitotic activity is also evident. The lesion is diffusely immunoreactive for cytokeratin and CD34, and demonstrates loss of INI1 protein by immunohistochemistry, supporting the diagnosis of epithelioid sarcoma.
Differential Diagnosis: Epithelioid sarcoma is often mistaken for a benign granulomatous process such as deep granuloma annulare or infectious granulomas. The greater cytologic atypia is a clue to the diagnosis, which can be supported by diffuse cytokeratin immunoreactivity that would not be identified in a benign granulomatous process. Epithelioid hemangioendothelioma also contains epithelioid neoplastic cells that label CD34 and cytokeratin. However, most of the neoplastic cells would demonstrate vacuolated, “blistered” cytoplasm and the stroma would have a more prominent myxoid appearance. Epithelioid hemangioendothelioma would also label vascular markers like ERG and CD31.
Incorrect
Answer: Epithelioid sarcoma
Histology: This is a multinodular proliferation of epithelioid cells within the dermis and subcutaneous tissue. Focally, the nodules form tight rounded clusters and are associated with central necrosis, simulating a necrotizing granuloma. However, the lesion does demonstrate greater cytologic atypia than would be expected for benign histiocytes, including rhabdoid cytology in several foci. Moreover, mitotic activity is also evident. The lesion is diffusely immunoreactive for cytokeratin and CD34, and demonstrates loss of INI1 protein by immunohistochemistry, supporting the diagnosis of epithelioid sarcoma.
Differential Diagnosis: Epithelioid sarcoma is often mistaken for a benign granulomatous process such as deep granuloma annulare or infectious granulomas. The greater cytologic atypia is a clue to the diagnosis, which can be supported by diffuse cytokeratin immunoreactivity that would not be identified in a benign granulomatous process. Epithelioid hemangioendothelioma also contains epithelioid neoplastic cells that label CD34 and cytokeratin. However, most of the neoplastic cells would demonstrate vacuolated, “blistered” cytoplasm and the stroma would have a more prominent myxoid appearance. Epithelioid hemangioendothelioma would also label vascular markers like ERG and CD31.
