[Kaposi's sarcoma. A vascular neoplasm of presumably viral origin. Histologic and ultrastructural characteristics]

Kaposi's sarcoma is a multiform mesenchymal neoplasm of uncertain histogenesis but of possible viral origin. Several anatomo-clinical forms have been described the cutaneous nodular lesion being the most common and at highest frequency in equatorial Africa. Eighteen of such typical lesions were reported; their morphology was uniform and associated: 1) spindle cells, 2) an excess of vascular spaces composed of intratumoral intercellular slits and of intra and peritumoral well structured vessels, 3) a lymphoplasmocytic inflammatory infiltration. The lesions of the other and less common forms of Kaposi's sarcoma associated the same histological features in variable combination. At one end of the histological spectrum the lesions are essentially composed of irregular capillaries with few spindle cells, at the other end the tumor is a highly cellular neoplasm with few or no angiogenic features. The vascular structure of the typical lesions appeared clearly at the ultrastructural level. Most tumor cells were of endothelial type and formed cylinders with virtual or large central lumina, reminiscing of vascular sprouts. Pericyte-like cells were also present. In one the three ultrastructurally investigated cases, a tumor cell of the endothelial type contained intranuclear herpes virus like inclusions, group to which belongs the cytomegalovirus (CMV), a possible promoter of Kaposi's sarcoma.