Inclusion Criteria:  Patients must be 18 years of age or older; Patients must have had a pathologically confirmed supra-tentorial primary brain tumor Patients must have history of deep venous thrombosis (DVT) and/or pulmonary embolism (PE) Patients must have been treated with low molecule weight heparin for ≥ 5 days Patients must be able to provide written informed consent Patients must have non contrast CT that is negative for intra-cranial bleed at least 5 days post initiation of LMWH and prior to initiation (within 7 days) of Apixaban Must be decision by patient and his physician to convert to Apixaban  Exclusion Criteria:  Patients with a plan less than 6 months of anticoagulation for most recent DVT or PE Patients with allergic reaction to Apixaban Patients with active bleeding or high risk for bleeding contraindicating treatment with LMWH Patients with planned surgery in the next 2 weeks Patients previously treated with Apixaban Patients requiring Acetylsalicylic Acid (ASA) greater than165 mg/day at enrollment Patients requiring dual anti-platelet therapy (ASA plus clopidogrel or ASA plus ticlopidine) at enrollment. Subjects with transition for dual anti-platelet therapy or monotherapy prior to enrollment will be eligible for the study Patients who are compulsorily detained for treatment of either a psychiatric or physical (e.g. infectious disease) illness Any condition, which in the opinion of the investigator, would put the subject at an unacceptable risk from participating in the study Any other medical, social, logistical, or psychological reason, which in the opinion of the investigator, would preclude compliance with, or successful completion of, the study protocol Known active and clinically significant liver disease (e.g., hepatorenal syndrome) Known bacterial endocarditis Know uncontrolled hypertension: systolic blood pressure greater than 160 mm Hg or diastolic blood pressure greater than 100 mm Hg; (subjects who have a transient, higher blood pressure elevation associated with acute PE [upper limit: systolic blood pressure 200 mm Hg or diastolic blood pressure 100 mm Hg] may enter the study;) elevated blood pressure that is persistent 1 - 2 days after the index DVT or PE should be treated according to local guidelines