Malignant tumors are a high risk factor for venous thrombotic disease, and the literature reports a detection rate of malignant tumors of nearly 10% in patients with unexplained lower extremity DVT. Anticoagulation therapy for patients with malignant tumors is associated with a much higher risk of bleeding, and the chance of thrombus recurrence after discontinuation of anticoagulant drugs is higher than that of non-tumor patients. Therefore, anticoagulation with low molecular heparin is recommended for patients with malignant tumors with lower extremity DVT for at least 3 months and for as long as the malignancy is active.