Venous blood clots affect nearly a million Americans each year. Venous clots in the legs are called deep venous thrombosis (DVT) and are dangerous because they travel to the lungs where they cause blockages known as pulmonary emboli (PE). DVT and PE are called venous thromboemboli (VTE). Cancer is a risk factor with nearly 200,000 VTEs in cancer patients each year. The purpose of VTE treatment is to prevent the initial clot from spreading and to prevent new clots from forming. This is accomplished by thinning the blood, or anticoagulation. Without anticoagulation, VTEs recur and are often fatal.