TFPI and leukemia: TF is a transmembrane receptor that is constitutively expressed in tumors, i.e. human leukemias, lymphomas, adenocarcinomas, and sarcomas.3 TF also plays a role in cellular signaling, contributing to tumor growth and metastasis.3,4 The only known endogenous modulator of blood coagulation initiated by TF is tissue factor pathway inhibitor (TFPI)—a plasma Kunitz-type serine protease inhibitor.5,6 Growing evidence suggests the involvement of tumor-derived proteins, including heparanase, in activation of the coagulation system.