Venous thromboembolic disease is a common and potentially serious condition in oncology patients, and the NCCN guidelines on venous thromboembolism specifically address strategies for the prevention and treatment of VTE (venous thrombosis) in adult hospitalized patients with clinically established or suspected tumors. The potential relationship with tumors was first reported by Trousseau in 1865 and has been confirmed by the results of several studies in recent years. Pathophysiologic explanations for VTE in patients with tumors include a known hypercoagulable state (e.g., procoagulants such as tissue factor derived from tumor cells), damage to the vessel wall, and venous stasis due to direct external pressure on the vessel. However, the real reason for the close relationship between tumor and VTE is not clear. Foreign studies have shown that VTE is thought to increase the likelihood of death in tumor patients by a factor of 2-8. A recent autopsy summary suggests that VTE occurs in approximately 80% of medical oncology patients. To focus on the important issue of comorbid VTE in oncology patients, the NCCN formed an expert panel in 2005. the VTE panel (composed of representatives from multiple disciplines in the NCCN member groups) includes surgical oncologists, medical oncologists, hematologists, cardiologists, internists, and others. While most risk factors for the development of VTE are common among oncology patients, others are unique, including the presence of malignancy and the use of antineoplastic drugs, as well as endocrine therapy. Two case-control studies in populations reported that the presence of tumors increased the risk of VTE by a factor of 4 and 7, respectively. This result has been confirmed by several other studies. Recent diagnosis of tumor, tumor progression, and distant metastases also increased the risk of VTE. Some specific drugs for antitumor therapy are associated with an increased risk of VTE. These drugs are not listed in detail here. Numerous studies have shown that central venous catheter (CVC) is a risk factor for upper-extremity DVT (UEDVT), and the NCCN recommends that all adult oncology inpatients receive anticoagulation therapy without contraindications (Class 1 evidence). The Panel on Prophylactic Anticoagulation recommends that all hospitalized patients with a diagnosis of active tumor (or clinical suspicion of tumor presence) and no contraindications to anticoagulation receive prophylactic anticoagulation (Class 1 evidence). This recommendation is based on the assumption that exercise to reduce the risk of VTE in hospitalized oncology patients is inappropriate. Anticoagulation therapy should be administered throughout the hospitalization. High-risk oncology patients (e.g., after oncologic surgery) should be strongly considered for continued VTE prevention therapy after discharge. Several studies comparing different anticoagulation regimens used to prevent VTE in oncology patients have not clearly shown that one treatment regimen is particularly efficacious. For example, after elective major abdominal or pelvic surgery, there was no difference in the incidence of VTE and bleeding between patients treated with 40 mg of enoxaparin daily or a low dose of plain heparin three times daily for VTE prophylaxis. In addition, a Meta-analysis of randomized clinical trials found that the efficacy and safety of low molecular heparin and regular heparin for VTE prophylaxis in patients after general surgery were the same. However, the results of a recent nonrandomized, retrospective controlled study comparing the use of low-molecular dalteparin (5,000 units once daily) or low-dose regular heparin (5,000 units three times daily) for VTE prevention in high-risk patients undergoing surgery for gynecologic oncology suggests that the regimen of dalteparin is not optimal in these patients. In summary: Recognizing the high risk of VTE in oncology patients is the first step in preventing VTE, and the NCCN panel recommends VTE thromboprophylaxis in all hospitalized oncology patients without contraindications to this treatment. The experts also emphasized the need for a high level of vigilance for VTE in oncology patients, careful evaluation and follow-up of oncology patients suspected of VTE, and prompt treatment and follow-up of patients diagnosed with VTE, taking into account the patient’s tumor status and risk of subsequent recurrence.