OUTLINE: This is a randomized study. Patients are stratified according to prior chemotherapy within the past 3 weeks (yes vs no). Patients are randomized to one of two treatment arms. Arm I: Patients receive a single dose of standard heparin subcutaneously (SQ) followed by evaluation of tissue factor pathway inhibitor (TFPI) response at 5 and 10 minutes post injection. Arm II: Patients receive a single dose of enoxaparin SQ followed by evaluation of TFPI response as in arm I. Patients are followed monthly for 3 months.