In this study we report the histopathological features in a series of 88 biopsies from patients with cutaneous Kaposi's sarcoma; immunohistochemical examination for Factor VIII related antigen has been carried out on frozen and paraffin-embedded sections. The patient groups comprised 50 elderly patients, seven of whom were immuno-compromised, six patients with AIDS and one patient who had received a renal allograft. The findings were similar in these three groups. Histological staging was carried out with subdivision into stage I--patches characterized by angiomatoid and glomeruloid structures; stage II--plaques characterized by confluence of angiomatoid and glomeruloid structures and with spindle cells; and stage III--nodules in which the spindle cells were proliferative and frankly sarcomatous. Factor VIII related antigen was demonstrated in the central vessels of glomeruloid lesions whilst the surrounding vascular network contained both antigen-negative and antigen-positive vessels; in stage II and III lesions the spindle cells were consistently positive only in frozen section material. The findings were similar in the three patient groups. Our results suggest that Kaposi's sarcoma evolves from stage I through to stage III, that both blood vessels and lymphatic vessels are involved in the vascular proliferation and that the spindle cells are derived from vascular endothelium.
