This trial studies how well dalteparin works in preventing deep vein thrombosis (DVT) (blood clots) in participants with cancer. Dalteparin is a blood thinner that can treat blood clots and may prevent them from forming.

PRIMARY OBJECTIVES:

I. To determine the safety of dalteparin as prophylaxis against deep venous thrombosis (DVT) in orthopedic oncology patients.

II. To determine whether there are significantly increased bleeding complications at the surgical site after major oncologic operations in the lower extremity.

OUTLINE:

Participants receive dalteparin subcutaneously (SC) once daily (QD) starting 12-24 hours after surgery on post-operative day 1 until hospital discharge, about 7-10 days.

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.

4 weeks after surgery