Kaposi's sarcoma in renal transplant recipients. Ultrastructural and immunoperoxidase study of four cases.

Tissues from four cases of Kaposi's sarcoma developing in renal transplant recipients were studied by light and electron microscopic examination and by immunoperoxidase staining for Factor-VIII-related antigen. Ultrastructurally, the tumors in all four cases contained a variable mixture of cells, including endothelial cells, pericytes, fibroblasts, and myofibroblasts. These findings support the origin of Kaposi's sarcoma from primitive vasoformative mesenchyme. Immunoperoxidase staining for Factor-VIII-related antigen was limited to endothelial cells. In one case intracytoplasmic virus-like tubular complexes were seen. The significance of this finding is briefly discussed.