Biomarkers, Tumor/metabolism; Bone Neoplasms/drug therapy; Osteosarcoma/drug therapy; Piperazines/therapeutic use; Protein Kinase Inhibitors/therapeutic use; Pyrimidines/therapeutic use; Receptor, Platelet-Derived Growth Factor alpha/metabolism; Receptor, Platelet-Derived Growth Factor beta/metabolism; Adolescent; Adult; Aged; Becaplermin; Benzamides; Biomarkers, Tumor/genetics; Blotting, Western; Bone Neoplasms/metabolism; Bone Neoplasms/secondary; Cell Survival/drug effects; Child; Female; Humans; Imatinib Mesylate; Immunoenzyme Techniques; Immunoprecipitation; Male; Middle Aged; Mitogen-Activated Protein Kinases/metabolism; Osteosarcoma/metabolism; Osteosarcoma/pathology; Phosphorylation; Platelet-Derived Growth Factor/metabolism; Prognosis; Protein-Tyrosine Kinases/antagonists & inhibitors; Proto-Oncogene Proteins c-akt/metabolism; Proto-Oncogene Proteins c-sis; RNA, Messenger/genetics; RNA, Messenger/metabolism; Receptor, Platelet-Derived Growth Factor alpha/genetics; Receptor, Platelet-Derived Growth Factor beta/genetics; Reverse Transcriptase Polymerase Chain Reaction; Tumor Cells, Cultured