1. What is osteosarcoma? Osteosarcoma is a common primary malignant bone tumor, accounting for 20% of primary malignant bone tumors. It is mostly found in the epiphysis of long bones of the limbs, with the upper and lower parts of the knee joint being the most vulnerable. The mortality and disability rates of osteosarcoma are very high, and the negative impact on society and patient’s family is large. 2. What are the causes of this disease? The specific causes of osteosarcoma are not well understood, but some data show that the cause of the disease may be related to viruses; some osteosarcomas are caused by benign bone tumors, chronic osteomyelitis, and some are caused by radiation. Although exercise is not the direct cause of osteosarcoma, collision and strain caused by exercise may cause the tumor to progress. 3. What are the diagnostic methods of osteosarcoma? In the diagnosis of osteosarcoma, the combination of clinical manifestations, imaging and pathological biopsy should be emphasized to improve the positive rate and accuracy. Among them, X-ray radiography is a simple and practical auxiliary examination method, which can generally obtain the diagnosis. To be prudent, CT-guided pathology aspiration biopsy is an important examination method. The operation method has the advantages of simplicity, safety, accuracy and little damage, which is accepted by most patients. 4. What is the comprehensive treatment of osteosarcoma? Comprehensive treatment of osteosarcoma is a therapy that can take into account both systemic and local treatment. The first treatment for patients with osteosarcoma should ideally be effective in saving the patient’s limbs by treating the primary focus and saving the patient’s life by extinguishing the lung metastases. Clinical treatment cannot only emphasize the treatment of the primary focus, because no matter how good the local treatment is, it cannot control the development of pulmonary metastases or improve the survival rate. 5. What is limb-preserving treatment for osteosarcoma? Is the recurrence rate and metastasis rate of limb preservation surgery higher than amputation? Limb preservation therapy is to preserve the limb under the premise of complete removal of the tumor, and to adopt various methods including artificial prosthesis replacement to rebuild the function of the affected limb, so as to improve the quality of life of patients during their lifetime. Limb preservation therapy has become a highly recognized treatment modality for osteosarcoma, and it is also the direction that osteosarcoma clinicians are striving for. Current research data show that for patients who are eligible for limb preservation therapy, the local recurrence rate survival rate of limb preservation plus chemotherapy is the same as that of amputation plus chemotherapy. The efficacy of limb preservation therapy is inextricably linked to the development of neoadjuvant chemotherapy (preoperative chemotherapy). Effective preoperative chemotherapy can result in significant tumor shrinkage, improve surgical resection rate and reduce recurrence. 6. What is high-dose MTX chemotherapy? How is the safety guaranteed? High-dose methotrexate with formyltetrahydrofolate relief (HD-MTX-CF-R) is one of the most important regimens of chemotherapy for osteosarcoma. It is chemotherapy administered to patients with dosages of MTX that are tens or hundreds of times higher than the conventional dosage to improve the efficacy. Safety can be guaranteed as long as blood levels are monitored and laminar flow wards and hemodialysis conditions are available. The use of this protocol is technically demanding and requires a team of experienced and responsible medical and nursing staff, so we recommend that patients, should go to an experienced medical institution for standardized treatment. 7. Is it necessarily incurable once osteosarcoma pulmonary metastasis appears? For patients with osteosarcoma lung metastasis, we should fully utilize the available drugs, follow the principle of multidisciplinary comprehensive treatment, conduct regular imaging review, give surgery or γ-knife and supplement with regular and effective chemotherapy, which can make osteosarcoma lung metastasis achieve better treatment results. In recent years, through active treatment of this group of patients, the efficacy has been improving, and it is even reported abroad that about 40% of patients can have a survival of more than 5 years. Individual patients can achieve complete remission and long-term survival through chemotherapy.