Dalteparin in Preventing DVT in Participants With Cancer

Inclusion Criteria: * GROUP A * Metastatic disease, myeloma, lymphoma. * Pathologic fracture or impending pathologic fracture of the femur. * Intramedullary rod, plating, cementation, hip arthroplasty, or knee arthroplasty. * GROUP B * Primary sarcoma of bone or soft tissue of the lower extremity. * T2 tumor (\> 5 cm by \< 20 cm). * Radical resection of tumor, which may necessitate major bone or soft tissue reconstruction. Exclusion Criteria: * Presence of DVT on pre-operative screening ultrasound study. * Massive tumor (\> 20 cm in greatest dimension). * Amputation of the affected leg as treatment of tumor. * Estimated blood loss \> 2 liters during surgery. * Surgical drain output \> 500 cc of bloody fluid during first 8 hours. * International normalized ratio (I.N.R.) \> 1.3 pre-operatively or \> 1.5 post-operatively. * Platelet count \< 100,000 either pre-operatively or post-operatively. * Indwelling post-operative epidural catheter for pain control. * History of underlying bleeding disorder, such as hemophilia. * History of adverse reaction to heparin such as heparin-induced thrombocytopenia. * Severe liver or renal insufficiency. * History of hypertensive or diabetic retinopathy. * History of gastro-intestinal bleeding within 12 months. * Treatment with warfarin, clopidogrel, aspirin, nonsteroidal antiinflammatory drugs (NSAIDs), low molecular weight heparin (LMWH) or other anti-coagulants for conditions. * History of stroke. * Women of child bearing potential having a positive urine or serum pregnancy test (human chorionic gonadotropin \[hCG\]) at the time of pre-operative evaluation (within 7 days of surgery). * Women who are breastfeeding. * Hemoglobin \< 8.0 g/dL. * Platelet count \< 100,000/L. * Alanine aminotransferase \> 100 IU/L. * Aspartate aminotransferase \> 100 IU/L. * Direct bilirubin \> 0.5mg/dL. * Serum creatinine \> 2.0 mg/dL. * Patients taking COX-2 inhibitors. * Patients who have fragmented mechanical heart valves.