Ultrastructural findings in oral Kaposi's sarcoma (AIDS).

Ten biopsies of oral Kaposi's sarcoma were examined histologically and ultrastructurally. Histologically, early and late tumor stages could be differentiated. On the ultrastructural level, endothelial-like and spindle-shaped tumor cells were revealed. Tumor cells associated with vessel-like spaces showed partly interrupted basal membranes, Weibel-Palade bodies, desmosomes and tight-junctions, while spindle-shaped cells lacked these ultrastructural features of endothelial cells. Within the cytoplasm of endothelial-like cells, aggregates of tubular structures were observed. Histological and ultrastructural findings in oral Kaposi sarcoma are comparable to those of such other organs as skin and intestines. The ultrastructural findings indicate an endothelial origin, at least of endothelial-like tumor cells.