F2R and cancer: Following activation by extracellular proteinases, including members of the KLK family, PAR1 plays significant roles in many normal physiological processes, such as coagulation7, inflammation8, and vascular homeostasis9, but it also contributes to some inflammatory10 and cardiovascular pathologies, including atherosclerosis11, restenosis12, and thrombosis13, and to the progression of some cancers by stimulating cell migration and tissue invasion.