Inclusion Criteria:

• A histologic diagnosis of malignancy;
• At planned initiation of a new systemic chemotherapy regimen (including patients starting on first chemotherapy or patients previously treated but starting on a new regimen);
• A risk score for VTE ≥3 [assign score of 2 for very high risk sites of cancer (stomach, pancreas), score of 1 for high risk site (lung, lymphoma, gynecologic, bladder, testicular) and score of 0 for all other sites], hemoglobin <10 g/dL or planned use of erythropoiesis stimulating agents, platelet count ≥350,000/mm3, total leukocyte count > 11,000/mm3 or body mass index ≥ 35 kg/m2]. Any counts meeting criteria drawn within 2 weeks prior to enrollment are considered acceptable.
• Age 18 years or older
• Provide written, informed consent.

Exclusion Criteria:

• Active bleeding or at high risk of serious bleeding complication in the opinion of the investigator
• Diagnosis of primary brain tumor multiple myeloma, leukemia, or myelodysplastic syndrome
• Planned stem cell transplant
• Life expectancy < 6 months
• Known allergy to heparin or LMWH
• Incapable of daily self-injection
• Acute or chronic renal insufficiency with creatinine clearance < 30 mL/min
• History of heparin-induced thrombocytopenia
• Allergy to contrast agents
• Pregnancy
• Need for anticoagulant therapy
• Platelet count < 75,000/mm3