The purpose of this study is to develop indices predicting response to pre-operative chemotherapy in osteosarcoma patients. Histologic response to pre-operative chemotherapy is very important for the ultimate outcome of osteosarcoma patients. Conventional methods such as CT or MRI evaluating tumor response to chemotherapy is not so efficient in tumors like osteosarcoma. Instead, the investigators will test whether blood TGF-b1 levels, PET/CT findings, MRS findings as well as the level of NF-kB expression in tumor tissues can predict chemotherapy response in osteosarcoma.