For more than 50 years, heparin and vitamin K antagonists (VKAs) have been the anticoagulant drugs used to prevent and treat thrombosis. Low molecular weight heparins (LMWHs) are more recent and have been available for approximately 20 years. Patients with cancer are members of a unique patient population because of their high risk for thrombosis and the risk of anticoagulant-related bleeding. With the currently available antithrombotic agents, patients with cancer still have unmet needs in terms of the prevention and treatment of thrombosis. Although long-term LMWH is the treatment of choice for patients with cancer who have acute, symptomatic venous thromboembolism (VTE), some patients still experience recurrent VTE. More effective antithrombotic agents are needed for such patients. Convenient (ie, oral and with no laboratory monitoring), effective, and safe agents are needed to prevent thrombosis in patients taking chemotherapy and antiangiogenic drugs and in patients with central vein catheters. There are a number of new antithrombotic agents that have been studied in recent years and will soon be available for certain diseases. They target either activated factor X (ie, factor Xa) or activated thrombin, and some of them have potential therapeutic value in patients with cancer. In this article, the clinical research model used for the development of a new antithrombotic agent is discussed along with the results of recent trials that evaluate these new agents in high-risk populations.