Basement membrane in Kaposi's sarcoma: an immunohistochemical and ultrastructural study

Basement membranes were investigated in early angiomatous and late sarcomatoid stages of Kaposi's sarcoma (KS). Seven frozen skin biopsies of KS from five elderly Mediterranean people and one renal allograft recipient were labelled, using an immunoperoxidase technique, for basement membrane-specific macromolecules, laminin and type IV-collagen. Twenty-seven other frozen cutaneous lesions including haemangio and lymphangiosarcomas, benign vascular tumours, and various epithelial, melanocytic, fibrohistiocytic, fibrosarcomatous and muscular tumours were processed in the same way. In addition an ultrastructural study was performed in two cases of KS, one haemangiosarcoma and one lymphangiosarcoma. Intense labelling was observed for both type IV-collagen and laminin, which appeared closely co-distributed, in all areas of KS. Staining pattern was often regular and continuous around neoplastic vessels in early lesions of KS, as in benign vascular lesions, whereas in late nodular lesions large amounts of basement membrane components were present in intercellular spaces between densely aggregated spindle cells. In contrast, ultrastructural examination disclosed early disruption of basement membranes around neoplastic vessels, and occasional fragments of external lamina were seen at the interface between KS spindle cells and collagen. Similar results were obtained in angiosarcomas both by immunohistological and ultrastructural study. In the comparative group, laminin and type IV-collagen were present, in significantly fewer quantities and in various distinctive patterns, in epithelial, melanocytic, fibrohistiocytic and muscular tumors. This study deals with basement membrane modifications in early and late lesions of KS and provides further evidence in favour of the endothelial nature of the spindle cells of KS.