Macrophage-rich epithelioid angiosarcoma mimicking malignant melanoma

Cutaneous epithelioid angiosarcoma is a type of cutaneous angiosarcoma and usually arise both on the head or neck of the elderly.An 86-year-old male with an epithelioid angiosarcoma of the scalp that mimicked malignant melanoma.A large irregular dark grey-blue plaque with an adjacent speckled tan nodule was suggestive of a primary cutaneous malignant melanoma with adjacent in-transit metastasis. Both had a well-circumscribed growth pattern and were composed of numerous large epithelioid cells with scattered severe atypia and mitoses. The tumor was positive for S-100 protein and vimentin and negative for low- and high-molecular weight cytokeratins. However, at high power, the epithelioid cells with severe atypia were negative for S-100 protein, and abundant large epithelioid macrophages were responsible for the S-100 protein positivity. The malignant tumor cells were negative for HMB-45, positive for CD31 and Factor VIII-related antigen, and focally positive for CD34. A focus of infiltrative, classical angiosarcoma with irregular vascular channels lined with plump, anaplastic endothelial cells was then found deep to the epithelioid tumor.Macrophage-rich epithelioid angiosarcoma demonstrates abundant S-100 protein-positive epithelioid macrophages. This subset of epithelioid angiosarcoma may mimic malignant melanoma and may present as a pitfall in diagnosis.