Blood-borne tissue factor

Existing paradigms of coagulation have been challenged in recent years by new experimental evidence for the existence of intravascular (blood-borne) tissue factor (TF). A revised model of coagulation to explain the mechanisms of initiation and propagation of coagulation has been proposed, in which physiological hemostasis -- and probably certain types of pathological thrombosis -- are critically dependent on circulating intravascular TF. Accumulating evidence suggests that this form of TF may be predominantly associated with cell-derived microparticles (MPs), small membrane units shed from activated and/or apoptotic cells. However, other forms of circulating TF, including soluble form(s), and cell-bound forms may also contribute to the intravascular pool of TF. While these observations are leading to a renaissance in the interest in blood-borne TF in the pathogenesis of thrombosis associated with cancer, TF may play a critical role in several other malignant cell functions, including angiogenesis and metastasis. The purpose of this communication however is to review the theoretical and practical considerations to be considered in designing assay(s) that might be used to measure circulating TF procoagulant activity in cancer and other disease states.