Microscopic Features of Hepatic Angiosarcomas: High-grade areas are composed of highly atypical, large plump endothelial cells with hyperchromatic nuclei and prominent nucleoli. The tumor cells have spindle or epithelioid morphology. Tumor giant cells may be present. There is increased mitotic activity. Foci of hemorrhage and necrosis are frequently present. Solid areas of spindle cells may resemble fibrosarcoma. Well-differentiated areas show anastomosing vascular channels lined by minimally atypical endothelium that infiltrate through the liver parenchyma.
At the periphery of the lesion, tumor cells with plump hyperchromatic nuclei spread along the pre-existing sinusoids and other vascular structures replacing normal endothelial cells. Branches of portal or hepatic vein are frequently invaded. The native liver architecture is destroyed. Additional findings may include hepatocyte atrophy, steatosis, and bile stasis.