How are epithelioid hemangioendothelioma (EHE) and epithelioid angiosarcoma differentiated?

Updated: Dec 25, 2019
  • Author: Joseph F Tomashefski, Jr, MD; more...
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The distinction between EHE and epithelioid angiosarcoma is sometimes difficult because of overlapping histological features and a similar immunohistochemical profile. The differential diagnoses of each of these tumors are similar and include sarcomatoid or biphasic mesothelioma, pseudomesotheliomatous carcinoma, and various metastatic tumors to the pleura, including malignant melanoma and epithelioid sarcoma.

In general, EHE can be differentiated from epithelioid angiosarcoma based on the presence of myxohyaline matrix and large epithelioid cells with little pleomorphism and low mitotic activity in EHE, compared to the marked pleomorphism and atypia with numerous mitotic figures in epithelioid angiosarcoma. [32] Immunostains are not helpful since both tumors express endothelial markers. There is not a consistent classification for tumors with a predominantly low-grade pattern of EHE which also have focal high-grade areas resembling epithelioid angiosarcoma. Some authors consider EHE and epithelioid angiosarcoma to represent a continuous spectrum of epithelioid vascular sarcomas involving the pleura. [40, 97]

Histologically, on routine hematoxylin and eosin stains, EHE and epithelioid angiosarcoma are sometimes indistinguishable from sarcomatoid or biphasic mesothelioma. [55, 97] Subtle features such as amphophilic cytoplasm, inconspicuous nucleoli, and intracytoplasmic lumina containing erythrocytes may suggest EHE. An initial clue to the presence of an epithelioid vascular sarcoma is strong staining for vimentin with absent or weak staining for pankeratin. [45] The reverse is true for mesotheliomas, which nearly always stain strongly for cytokeratin and less strongly for vimentin.

Expression of cytokeratin in some cases of EHE or angiosarcoma may cause confusion. Likewise confusing are the presence of cytokeratin-positive reactive submesothelial fibroblasts, which give a biphasic appearance, simulating mesothelioma. Immunostains for endothelial markers such as CD34, CD31, and factor VIII–related antigen are key to the diagnosis, since mesotheliomas rarely express these antigens.

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