Vascular tumors in the region of the breast.

Three vascular tumors in the breast region with different degrees of differentiation are presented. The first neoplasm is a haemangiosarcoma (of the vascular neoplasms, these tumors are the type which occur most frequently in the breast). Haemangiosarcomas show an infiltrative growth of atypical blood capillaries, frequently with formation of highly cellular and solid capillary sprouts. Ultrastructurally, the tumor cells are characterized as endothelial, also in the region of the capillary sprouts. The second tumor (an angiosarcoma in Stewart-Treves-syndrome, STS) is characterized by an intensive endothelial proliferation. Solid spindle-celled regions are also found in which the tumor cells correspond to undifferentiated mesenchymal cells, but other cells possessing properties of smooth muscle cells and pericytes may be found. The third tumor corresponds light and electron microscopically to a haemangiopericytoma of the soft tissue. The pericytic character of the tumor cells is most clearly seen in the immediate vicinity of the vessels. With increasing distance from the capillaries, the tumor cells take on the characteristics of fibroblasts. The tumors reflect the diversity of the angioplastic differentiation potential of the mesenchyme.