Consistent elevations of plasma von Willebrand factor antigen were observed in otherwise healthy elderly patients with Kaposi's sarcoma. The elevations were predominantly of the endothelial cell-derived antigen, as opposed to the factor VIII procoagulant, with resultant elevations in the antigen/procoagulant ratios. Lesser elevations were seen in a group of age-matched control subjects who did not have Kaposi's sarcoma or intercurrent illness. The greater elevations in plasma von Willebrand factor antigen therefore appear to be the direct consequence of the presence of Kaposi's sarcoma cells. Our findings also suggest that there is a direct relationship between tumor load and degree of von Willebrand factor antigen elevation.
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