Epithelioid angiosarcoma: a brief diagnostic review and differential diagnosis.

Epithelioid angiosarcoma is a highly aggressive endothelial cell malignancy, most commonly arising in the deep soft tissues, but a variety of primary sites, including the adrenals, thyroid, skin, and bone, are encountered. On hematoxylin-eosin-stained sections, the pathologist encounters sheets of large, mildly to moderately pleomorphic epithelioid cells, with abundant eosinophilic cytoplasm, vesicular nuclei, and prominent nucleoli. Obvious vasoformative foci may not be present, creating confusion with metastatic carcinomas, malignant mesothelioma, melanoma, anaplastic lymphoma, epithelioid peripheral nerve sheath malignancies, and epithelioid sarcoma. Moreover, malignancies with apparent vascular differentiation must be distinguished from less aggressive vascular neoplasms, including epithelioid hemangioendothelioma. Given the range of clinical presentation, the diversity of primary sites, and the nonspecific initial histopathologic appearance, here we review the histologic findings and immunohistochemical profiles of epithelioid angiosarcoma and neoplasms in its differential diagnosis.