A malignant tumor originating from the endothelial cells of lymphatic vessels. Most lymphangiosarcomas arise in an arm secondary to radical mastectomy but they sometimes complicate idiopathic lymphedema. The lymphedema has usually been present for 6 to 10 years before malignant changes develop. (From Dorland, 27th ed; Holland et al., Cancer Medicine, 3d ed, p1866)

A rare malignant neoplasm characterized by rapidly proliferating, extensively infiltrating, anaplastic cells derived from blood vessels and lining irregular blood-filled or lumpy spaces. (Stedman, 25th ed)