1, the concept of neoadjuvant chemotherapy Adjuvant chemotherapy was first started in the 1960s, mostly after surgery. Neoadjuvant chemotherapy started in 1973. At that time, it took a long time (up to three months) for the artificial prosthesis to be fabricated. Drs. Rosen and Marcove at MemorialSloan-Kettering Oncology Center administered preoperative chemotherapy to some patients with osteosarcoma who were indicated for large tumor resection and artificial prosthesis replacement surgery to prevent tumor progression while waiting for the artificial joint to be fabricated. In 1979, Rosen et al. formally introduced the concept of neoadjuvant chemotherapy, in which he emphasized that neoadjuvant chemotherapy is not a simple model of “preoperative chemotherapy + surgery + postoperative chemotherapy”, but includes a comprehensive assessment of the patient and the tumor after preoperative chemotherapy. It involves a comprehensive assessment of the patient and the tumor after preoperative chemotherapy: the reduction of pain, the degree of mass reduction, and whether the lesion borders become clear on imaging, whether there is an increase in osteosclerosis, and whether there is a decrease in neovascularization of the tumor. Nowadays, the concept of neoadjuvant chemotherapy has been widely recognized. On the basis of postoperative adjuvant chemotherapy, most new chemotherapy regimens add preoperative chemotherapy, which has become the standard mode of treatment for malignant bone tumors. 2. Role of neoadjuvant chemotherapy 1) Early systemic treatment to eliminate potential micro metastases:Take osteosarcoma as an example, when the diagnosis is made clinically, 80% of these patients have already developed lung metastases, so the treatment should first take high-dose chemotherapy. Wittig et al. 2002 reported that the use of neoadjuvant chemotherapy resulted in limb-sparing surgery in 90-95% of patients with osteosarcoma, with a five-year survival rate of 60%-80%. (2) Assessment of the effect of preoperative chemotherapy to guide postoperative chemotherapy: the histological response of the tumor to chemotherapy is the most important factor affecting long-term prognosis, and those found to respond poorly to neoadjuvant chemotherapy are switched to other cytotoxic agents (salvage chemotherapy) after surgery. Neoadjuvant chemotherapy emphasizes preoperative chemotherapy for 6-10 weeks, followed by tumor resection and postoperative chemotherapy regimens based on the degree of tumor tissue necrosis. If the tumor necrosis rate is greater than 90%, the five-year survival rate can reach 80%-90% if the original chemotherapy regimen is continued after surgery; while the five-year survival rate is less than 60% if the necrosis rate is less than 90%, the postoperative chemotherapy regimen should be adjusted. (3) Reduce the tumor and the reactive zone around the tumor to improve limb preservation surgery: high-dose chemotherapy can kill the tumor cells in several levels, and a large area of necrosis occurs in the primary foci, which reduces the tumor volume and reduces the chance of intraoperative tumor cell spread, the reactive edema zone around the tumor decreases, the blood vessels are reduced, the cutting edge is safer, more muscles can be preserved, and the function of the limb after limb preservation surgery is good and the chance of recurrence is small. (4) Allow sufficient time to design limb preservation plan and make prosthesis: The site, scope and nature of bone tumor are not exactly the same in each case, so it is difficult to prepare prosthesis with uniform standard. During this time of preoperative chemotherapy, it is possible to carefully design the prosthesis and surgical plan for the patient without delaying the patient’s treatment.