• Active malignancy defined as histologically confirmed diagnosis within last 6 months or received any cancer directed therapy within the last 6 months.

• Radiologically confirmed newly diagnosed symptomatic deep vein thrombosis or pulmonary embolism within 28 days of enrollment. Includes proximal lower-limb DVT or symptomatic PE. Upper extremity or catheter-associated thrombosis will be included, as will distal lower extremity DVTs.

• Platelet count \< 75,000/ml (prior to platelet transfusion) within 28 days of VTE diagnosis.

• Platelet count responsive to transfusion if previously administered (defined as an average platelet increase of at least 10,000/ml over the last 3 transfusions.

• No evidence of active hemorrhage.

• No recent history of major hemorrhage (requiring transfusion, hospitalization or intervention) within the last 12 months.

• No known brain metastases.

• Age ≥18 years. Because no dosing or adverse event data are currently available on the use of apixaban in participants \<18 years of age, children are excluded from this study, but will be eligible for future pediatric trials.

• ECOG performance status ≤2

• Participants must have adequate organ and marrow function as defined below:

‣ Total bilirubin ≤ institutional upper limit of normal (ULN)

⁃ AST(SGOT)/ALT(SGPT) ≤3 × institutional ULN

⁃ Glomerular filtration rate (GFR) ≥25 mL/min/1.73/m2

• Human immunodeficiency virus (HIV)-infected participants on effective anti-retroviral therapy with undetectable viral load within 6 months are eligible for this trial.

• For participants with evidence of chronic hepatitis B virus (HBV) infection, the HBV viral load must be undetectable on suppressive therapy, if indicated.

• Participants with a history of hepatitis C virus (HCV) infection must have been treated and cured. For participants with HCV infection who are currently on treatment, they are eligible if they have an undetectable HCV viral load.

• The effects of apixaban on the developing human fetus are unknown. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after completion of apixaban administration.

• Ability to understand and the willingness to sign a written informed consent document.