Exposure to anticoagulants in vivo decreases platelet release of VEGF. (A) VEGF concentration in the releasate generated from the platelets of patients in response to activation with ADP or exposure to MCF-7 cells with and without LMWH anticoagulation. (B) VEGF concentration in the releasate generated from the platelets of patients in response to activation with ADP or exposure to MCF-7 cells with and without coumadin anticoagulation. (C) VEGF concentration in the releasate generated from the platelets of patients in response to activation with ADP or exposure to MCF-7 cells with and without fondaparinux anticoagulation. (D) Schematic model of tumor cell and platelet communication and impact on angiogenesis. In our model, platelets come in contact with tumor cells in the vasculature, which activates the platelets to release angiogenic proteins that can then affect tumor cell growth, the impact of which is diminished in the presence of anticoagulants (n = 5 for each treatment group).