Angiosarcoma is a rare and highly aggressive tumor of endothelial origin. The molecular mechanisms driving angiosarcoma growth have not been fully elucidated, although autocrine stimulation by vascular endothelial growth factor (VEGF) secretion may play a role in the pathogenesis of this tumor. We identified a patient with a very rare form of angiosarcoma arising from the retroperitoneum. Immunohistochemical analysis demonstrated widespread up-regulation of the hypoxic response pathway as a mechanism of enhanced VEGF expression. Disordered regulation of the hypoxic response pathway can result in the expression of factors such as VEGF and erythropoietin, which may promote autocrine tumor growth in angiosarcoma.