Fibrinogen is well known as a coagulation protein of liver origin, which circulates in plasma at a concentration of 2 to 4 g/l. Fibrinogen/fibrin deposited in tumorous tissues arises exclusively from the extravasated plasma. The plasma extravasated from leaky blood vessels contains not only fibrinogen, but also some other coagulation factors present in blood. As many types of malignant cells are capable of producing and secreting plasminogen activator, which induces fibrinolysis, the stabilized or unstabilized nature of extravascular fibrin deposits in the tumor stroma is a question of high biological significance. Tumor matrix serves as a “seat of war” for these opposing forces, i.e., the extent of fibrin deposition is a reflection of the balance between coagulation and fibrinolytic events. The network, composed of extracellular matrix macromolecules, is encrusted by fibrin deposits in the majority of spontaneously arising as well as transplantable human and animal tumors, although the extent of fibrin deposition varies highly in different types of malignancies.
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