Kaposi's sarcoma: immunohistologic evidence for an endothelial origin.

Factor VIII-related antigen (VIIIR-Ag), a marker for endothelial cells, was used to explore the histogenesis of Kaposi's sarcoma. Formaldehyde-fixed, paraffin-embedded routine histologic sections from 37 cases of Kaposi's sarcoma and from 16 other spindle-cell tumors of the skin were stained for the presence of VIIIR-Ag, using an immunoperoxidase technique. Positive reactions were noted in all cases of Kaposi's sarcoma regardless of their histologic variations. Although the intensity of reaction was greater in cells that lined vascular channels and blood-filled clefts, many intertwining spindle cells contained VIIIR-Ag in their cytoplasm as well. Since VIIIR-Ag is elaborated only by endothelial cells and megakaryocytes, positive immunologic reaction for this factor in the cells of Kaposi's sarcoma strongly supports an endothelial derivation.