Malignant tumors originating from mesenchymal tissue (including connective tissue and muscle) are called "sarcomas". They often occur in the skin, subcutaneous tissue, periosteum and both ends of long bones. For example, fibrosarcoma grows rapidly, and in the late stage of the tumor, there is often necrosis and bleeding. The cross-section is gray-red and the texture is uniform and fine like raw fish meat. Osteosarcoma is more common in young people and is prone to occur at the ends of the long bones of the limbs, especially the lower end of the femur, the upper end of the tibia and the upper end of the humerus. Osteosarcoma develops rapidly and has a short course of disease. It starts to grow in the cortex and can gradually develop into the bone marrow cavity. Sometimes it breaks through the periosteum and invades the surrounding soft tissue, which can easily cause pathological fractures. Other common ones include leiomyoma, lymphosarcoma, synovial sarcoma, etc. Hematogenous metastasis can occur in the early stage. Sarcoma is a malignant tumor lesion.