Epithelioid angiosarcoma histology. The tumor is composed of large, epithelioid cells with vesicular nuclei and prominent nucleoli (A), with fibrous stroma (B). (C) Vascular formation and malignant endothelial cells containing erythrocytes are observed. (D) Increased mitotic activity is observed. Immunohistochemically, tumor cells express cytokeratins AE1/AE3 (E) and the vascular marker CD31 (F).