Subcutaneous hemangiosarcomas in a rhesus macaque (Macaca mulatta)

Hemangiosarcoma is a malignant tumor of vascular endothelial cell origin. T he occurrence of hemangiosarcoma in nonhuman primates has been rarely docum ented. An adult male rhesus monkey was reported having a firm subcutaneous swelling, approximately 4.5 cm in diameter, on the ventral midline of the a bdomen. Fine-needle aspiration, microbial culture, biopsy, radiographs, exp loratory laparotomy, histopathology, immunohistochemistry, hematology, and serology were performed. A second subcutaneous mass approximately 4.5 x 4.0 x 2.7 cm developed on the ventral midline several weeks later. A fine-need le aspirate of the first mass consisted of numerous erythrocytes with few p olymorphonuclear cells and lymphocytes. Histopathology showed foci of spind le-shaped cells surrounding the vascular spacer. Many spindle-shaped cells had prominent nucleoli, and mitotic figures could occasionally be seen. Imm unohistochemical staining of the masses for Factor VIII-related antigen, an endothelial cell and tumor marker, yielded positive results. Both masses w ere consistent with hemangiosarcoma.