What is the purpose of preoperative chemotherapy? Neoadjuvant chemotherapy is preoperative chemotherapy with drugs, followed by chemotherapy followed by surgical treatment, and postoperative chemotherapy is continued by adjusting the chemotherapy regimen according to the necrosis rate of the tumor. The purposes of performing neoadjuvant chemotherapy include: 1. Pre-operative chemotherapy is mainly to eliminate the possible micro-metastases, including those in the blood; 2. Pre-operative chemotherapy will minimize the primary lesions and eliminate the edematous area to make the tumor boundary clearer, which is conducive to surgery to remove the tumor more completely; 3. Judging the effect of chemotherapy for tumor and facilitating the formulation of chemotherapy plan after surgery. The cut specimen can be diagnosed pathologically to check the tumor necrosis rate, and then judge the effect of chemotherapy before surgery. When the tumor necrosis rate is >90%, it proves that the preoperative chemotherapy program is effective and can be continued after surgery; when the tumor necrosis rate is <70%, it means that the postoperative chemotherapy needs to consider adjusting the program. When is neoadjuvant chemotherapy given? How long does chemotherapy need to be given? Once the pathological examination confirms the diagnosis of osteosarcoma, patients need to undergo chemotherapy immediately, the sooner the better. And after 3 cycles of preoperative chemotherapy, surgery can be started. The characteristic chemotherapy regimen of Beijing 301 Hospital is: 3 cycles of preoperative chemotherapy are implemented, that is, about 3 months of chemotherapy before surgery. Nowadays, international chemotherapy regimens, such as the Rosen regimen in the United States and the N-series regimen in Italy, also carry out about 3 cycles of preoperative chemotherapy.