Epithelioid angiosarcoma of deep soft tissue: a distinctive tumor readily mistaken for an epithelial neoplasm.

We report eight cases of epithelioid angiosarcoma arising in deep, usually intramuscular soft tissue. All the patients were men (mean age, 58). All the lesions arose in a limb or limb girdle. Cardinal morphologic features were the diffuse, sheetlike growth pattern, with only focally apparent vascular differentiation, and epithelioid tumor cells with a degree of intracytoplasmic vacuolation/lumen formation. Immunohistochemically, all eight cases coexpressed keratin as well as endothelial markers. In three cases, endothelial differentiation was confirmed ultrastructurally. Clinically, deep-seated epithelioid angiosarcomas are high-grade neoplasms that rapidly develop metastases. These findings expand the range of recognized epithelioid endothelial tumors and provide further evidence of keratin expression by such lesions. The presence of intracytoplasmic lumina/vacuoles (sometimes containing red blood cells) combined with the characteristic reticulin pattern and striking positivity for Factor VIII-RAg provide the clearest means of distinction from an epithelial metastasis.