This study is a single-arm, phase IV trial, of apixaban as treatment of venous thrombosis in patients with cancer. The current standard treatment of venous thrombosis in cancer patients is subcutaneous injections with low molecular weight heparin. During the last 5 years several new direct acting oral anticoagulants have been tested out as treatment of venous thrombosis. But very few cancer patients were included in the phase III clinical trials of the direct acting oral anticoagulants. Thus, there is a lack of information on how cancer patients with venous thrombosis will respond to treatment with direct acting oral anticoagulants. The current study will investigate the direct acting oral anticoagulant apixaban in cancer patients with venous thrombosis.

Inclusion Criteria:

• A diagnosis of cancer, other than basal-cell or squamous-cell carcinoma of the skin, within six months before enrollment. Any treatment for cancer within the previous six months, or recurrent or metastatic cancer.
• Objectively verified venous thrombosis
• Informed consent

Exclusion Criteria:

• Anticoagulant therapy prior to trial entry for > 96 hours
• Severe thrombocytopenia (platelets <50·109/L)
• Severe renal failure - creatinine clearance <30 ml/min
• The patients will be treated with catheter based thrombolysis for deep venous thrombosis or systemic thrombolysis for severe pulmonary embolism
• Pregnancy or breastfeeding.
• Childbearing potential without proper contraceptive measures
• Drug abuse or mental disease that may interfere with treatment and follow-up.
• Severe malabsorption so that oral treatment are expected to have reduced effect
• Mechanical heart valves
• Known allergy to apixaban
• Active bleeding or severe risk of bleeding so that the risk of bleeding is considered a greater danger than the risk of not treating the venous thrombosis
• Clinically significant liver disease (e.g., acute hepatitis, chronic active hepatitis, or cirrhosis)
• Concomitant use of strong cytochrome P-450 3A4 inhibitors (e.g., human immunodeficiency virus protease inhibitors or systemic ketoconazole, voriconazole or posaconazole) or inducers (e.g., rifampicin, carbamazepine, or phenytoin). Fluconazol is allowed.