Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Osteosarcoma is the most common primary malignancy of bone. Osteosarcoma accounts for 20% of primary bone malignancies. There is a preference for the metaphyseal region of tubular long bones. 50% of cases occur around the knee. It is a malignant connective (soft) tissue tumor whose neoplastic cells present osteoblastic differentiation and form tumoral bone. Osteogenic sarcoma is the sixth leading cancer in children under age 15. Osteogenic sarcoma affects 400 children under age 20 and 500 adults (most between the ages of 15-30) every year in the USA. Approximately 1/3 of the 900 will die each year, or about 300 a year. A second peak in incidence occurs in the elderly, usually associated with an underlying bone pathology such as Paget''s disease, medullary infarct, or prior irradiation. Although about 90% of patients are able to have limb-salvage surgery,complications, such as infection, prosthetic loosening and non-union, or local tumor recurrence may cause the need for further surgery or amputation.