Lymphaticovenous differentiation in Kaposi's sarcoma. Cellular phenotypes by stage.

The histogenesis of Kaposi's sarcoma was investigated by immunohistochemical staining of 20 skin specimens that represented four main histologic stages. The early phase of Stage 1 contained lymphatic-like clefts lined by endothelial cells with thin, discontinuous basement membranes shown by anti-laminin, absent Factor VIII-related antigen reactivity (FVIIIRAg), and only rare staining with dilute Ulex europaeus agglutinin I (UEA-I). In the late phase of Stage 1, the clefts developed into anastomosing, blood-filled channels, and the basement membrane became complete. Endothelial marker reactivities were not definitive, but weak staining with UEA-I and variable staining for FVIIIRAg characterized the spindle cells of Stage 2. However, spindle cells in monomorphic nodules were individually enclosed by immunoreactive laminin. The sequence of events, particularly in light of previous angiographic findings of lymphaticovenous union, suggests a disturbance in lymphaticovenous differentiation in Kaposi's sarcoma. Sclerotic closure of channels unable to maintain competent blood flow may select against lymphendothelial traits in the developing spindle cell nodule.