Ultrastructural Characteristics of Kaposi's Sarcoma

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Abstract
The uncertainty which exists on the histogenesis of Kaposi's sarcoma is emphasized and the pertinent literature is briefly reviewed, with particular reference to electron microscopic studies. The results of an investigation on the fine structure in 6 cases of the disease are presented and the characteristic features of the two principal types of cellular elements, endothelial-like and spindle cells, are described. The relevant aspects observed were a clearly outlined basement membrane, vesicles due to pinocytosis, dense granules presumably due to erythrophagocytosis and, most interesting because it had never been recognized before, the presence of cytoplasmic filaments 90–110 Å thick, which show considerable variation in number, distribution, course and direction. These filaments appear to be similar to those that have been shown in endothelial cells and seem structurally identical to leiomyofilaments. In discussing the significance of these findings, a correlation is made with the results of previously reported electron microscopic studies and the hypothesis is postulated that the tissue of Kaposi's sarcoma originates from mesenchymatous elements which may develop into cells either of the endothelial-like and of the leiomuscular-like type.