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Thromboembolic events are common in patients with cancer, make patients management more complicated, and are associated with increased mortality.The risk of thromboembolic events in cancer patients varies according to the type of malignancy and disease stage, and it is increased by surgical and non-surgical treatments.Cancer chemotherapy has been known to both amplify the known prothrombotic effect of cancer cells and to damage vessel wall directly,and is increasingly recognized as a risk factor for thromboembolic complications.Venous thromboembolism (VTE)is a frequent complication in hospitalized and bedridden patients with cancer, and even though specific studies in this setting are lacking, international guidelines recommend antithrombotic prophylaxis for VTE in these patients.In the last few years, some studies were performed to evaluate the role of thromboprophylaxis in patients with cancer in the outpatient setting.Two recent systematic reviews evaluated the efficacy and safety of parenteral or oral anticoagulants in ambulatory patients with cancer and no indication for prophylaxis.According to these reviews, the absolute risk increase of bleeding with warfarin outweighs the absolute risk reduction of VTE, while for parenteral anticoagulants a high-quality evidence of a reduction in VTE was found, with larger absolute effects than any plausible increase in risk of major bleeding.Further, there is a possible but still not convincing mortality benefit in specific categories of patients, namely those with small cell lung cancer.Following these findings, the 2012 Guidelines for antithrombotic treatment by the American College of Chest Physicians suggest prophylactic dose of low-molecularweight heparin or unfractionated heparin over no prophylaxis in outpatients with solid tumors who are at low risk of bleeding, and who have additional risk factors for VTE (previous thrombosis, immobilization, hormonal therapy,angiogenesis inhibitors, thalidomide and lenalidomide).As for ambulatory cancer patients undergoing chemotherapy,two large randomized trials (Agnelli & Gussoni, Lancet Oncology 2009 Agnelli, N Engl J Med 2012) have documented a significant reduction of thromboembolic events in patients receiving parenteral anticoagulants and with a number of tumor types.Future studies should focus on patients at high risk of VTE, such as those identified through the use of scores that have been recently proposed to optimize patient risk stratification.