A malignant tumor arising from the endothelial cells of the blood vessels. Microscopically, it is characterized by frequently open vascular anastomosing and branching channels. The malignant cells that line the vascular channels are spindle or epithelioid and often display hyperchromatic nuclei. Angiosarcomas most frequently occur in the skin and breast. Patients with long-standing lymphedema are at increased risk of developing angiosarcoma.
In rare instances, angiosarcoma can involve the small intestine or other parts of the gastrointestinal tract, particularly in older adults with uterine or urinary bladder cancer previously treated by irradiation.
Grossly, angiosarcoma forms a haemorrhagic, transmural, often ulcerated mass that often extends into mesentery. The lesions may be multifocal and/or metastases, e.g. from soft tissues of the head and neck.
Histologically, the irregular anastomosing vascular channels are lined by atypical spindled to epithelioid endothelial cells with variable mitotic activity. Although most are high-grade, isolated examples are well-differentiated and low-grade.
Immunolabelling is positive in nearly all cases for CD31 (membrane pattern), but more variable for CD34 and FVIII-related antigen. Keratins can be present, especially in epithelioid variants
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