Enoxaparin Thromboprophylaxis in Cancer Patients With Elevated Tissue Factor Bearing Microparticles

Inclusion Criteria: * Histologically confirmed malignancy that is metastatic or unresectable and for which standard curative therapies do not exist. Eligible malignancies include: * Adenocarcinoma of the pancreas (locally advanced or metastatic) * Colorectal (stage IV) * Non-small cell lung (unresectable stage III or IV) * Relapsed ovarian or stage IV * Surgically unresectable or metastatic gastric adenocarcinoma * First or second line therapy (within 4 weeks of initiating therapy). * Minimum age 18 years * Life expectancy of greater than 6 months * ECOG Performance Status 0, 1, or 2 (Karnofsky 60% or greater). * Participants must have normal organ and marrow function as outlined in the protocol. Exclusion Criteria: * Participants may not be receiving any other study agents. * Known brain metastases should be excluded from this clinical trial because of their poor prognosis and higher potential for intracranial hemorrhage. * Prior history of documented venous thromboembolic event or pulmonary embolism within the last 5 years years (excluding central line associated events whereby patients completed anticoagulation \> 3 months previously) * Active bleeding or high risk for bleeding (e.g. known acute gastrointestinal ulcer) * Any history of significant hemorrhage (requiring hospitalization or transfusion) outside of a surgical setting within the last 5 years * History of allergic reactions attributed to compounds of similar chemical or biologic composition to enoxaparin or heparin. * History of heparin-induced thrombocytopenia * Presence of coagulopathy (PT or PTT\> 1.5 x upper limit of normal) * Familial bleeding diathesis * Known diagnosis of disseminated intravascular coagulation * Currently receiving anticoagulant therapy * Current use of aspirin (\>81mg daily), Clopidogrel (Plavix), cilostazol (Pletal), aspirin-dipyridamole (Aggrenox), or regular use of non-steroidal anti-inflammatory agents more than twice weekly. Maximum dose of ibuprofen is 400mg no more than twice per week. * Uncontrolled intercurrent illness including, but not limited to, ongoing active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements.