Postmastectomy angiosarcoma (Stewart-Treves syndrome). Light-microscopic, immunohistological, and ultrastructural characteristics of two cases.

Two cases of postmastectomy angiosarcoma were characterized morphologically and immunohistologically using markers for epithelial (anti-keratin antibodies) and endothelial cells (anti-vimentin antibodies, anti-Factor VIII-related antigen antibodies and Ulex europaeus I lectin). In both cases, the angiosarcoma had developed in a lymphedematous arm, 10 and 16 years after the mastectomy, and both patients died with metastatic angiosarcoma within 1 year. Both mammary tumors were adenocarcinomas, showing keratin-positive tumor cells, whereas the angiosarcomas cells were keratin-negative but vimentin-positive. The best-differentiated vascular lumina in the angiosarcomas were positive for Factor VIII-related antigen (FVIIIR:Ag), whereas most of the tumor cells reacted with Ulex europaeus I-lectin (UEA I), a recently introduced marker for endothelial cells. The carcinomas, on the other hand, were negative for FVIII R:Ag and did not bind UEA I, except the non-neoplastic vessels of the tumors. Ultrastructurally, the tumor cells showed prominent pinocytic vesicles and cell-cell junctions, but no Weibel-Palade bodies. The results corroborate the conclusions of endothelial origin of these tumors and rule out their derivation from the primary mammary carcinomas. The results also suggest that immunohistochemical markers for epithelial and endothelial cells can be used as diagnostic aids in distinguishing these neoplasms.