This 14-year-old white male first experienced mild pain in the left knee after playing baseball, approximately two months prior to admissionago. The pain persisted in an intermittent fashion, and was described as being somewhat worse at night. Approximately until approximately two weeks prior to admission, when the pain increased significantly and was accompanied by marked swelling and loss of considerable motion of the knee joint. These symptoms were accompanied by a history of He also had decreased appetite, lethargy, and a 10-pound weight loss. On physical examination, the left knee was enlarged diffusely, firm, and non-tender. Following Radiographic and biopsy, the results confirmed a diagnosis of osteosarcoma. The patient was subjected to underwent surgical removal of the distal femur and knee with placement of a prosthetic knee joint and bone grafts. The distal diaphysis of the femur and adjacent soft tissues were involved in a 15 x 10 x 10-cm mass. The cut surface of the mass was fleshy white, with focal areas of hemorrhage.