Cancer Chemotherapy-Related Thrombotic Thrombocytopenic Purpura: Biological Evidence of Increased Nitric Oxide Production

The occurrence of thrombotic thrombocytopenic purpura (TTP) in cancer patients receiving chemotherapy has been well established; although this entity is rare, its clinical importance seems to be growing. We describe 3 cases of TTP developing in cancer patients receiving different chemotherapeutic regimens. Using a sensitive high-performance liquid chromatographic method, we evaluated the stable nitric oxide end products, nitrite and nitrate, in the plasma of these patients. Nitric oxide is one of the key components involved in maintaining the normal nonthrombogenicity of the vascular endothelium. In our 3 patients, we found increased nitrate titers that were substantially higher than those observed in patients with de novo TTP. The observed increased release of nitrate could be interpreted as the consequence of massive disruption of endothelial integrity, with consequent passive nitric oxide release in vivo, or an adaptive mechanism of the endothelium to compensate for diffuse microvascular occlusion. The 2 mechanisms may both be involved, but the normal titers of nitric oxide end products in de novo TTP suggest that the former mechanism is more important, at least in cancer chemotherapy–related TTP.