 Some cancer patients starting a new chemotherapy regimen are likely to develop blood clots, also known as venous thromboembolism VTE. Blood clots can cause symptoms and can occasionally be life-threatening. The purpose of this study is to determine if a daily injection of a blood-thinner, dalteparin, for 12 weeks can safely and effectively reduce the frequency of blood clots. Dalteparin is currently approved for prevention of blood clots following surgery and in hospitalized patients but not specifically for cancer outpatients. 