Currently, the diagnosis of osteosarcoma in clinical settings primarily relies on a combination of clinical symptoms, imaging studies, and pathological findings. Clinically, osteosarcomas commonly occur in the distal femur, proximal tibia, and lower end of the humerus, manifesting as localized persistent pain, nocturnal pain, and swelling, often accompanied by superficial venous engorgement and increased skin temperature. Systemic symptoms of cachexia may appear, and even pathological fractures. Imaging is indispensable, revealing osteoblastic, osteolytic, or mixed osteolytic lesions, usually with a pronounced periosteal reaction, Codman's triangle (a common sign of malignancy), or sunburst patterns. Magnetic resonance imaging (MRI) is very important for diagnosing bone tumors as it can indicate the tumor's boundaries and the extent of erosion. Additionally, PET-CT and radioactive isotope scanning are considered crucial for tumor diagnosis. Pathological examination is currently regarded as the gold standard for diagnosing osteosarcoma. This involves a biopsy, usually taking a small part of the tumor for examination from a molecular biology perspective. However, when performing a biopsy, it is important to note two things: first, it is preferable to take the biopsy intraoperatively; second, if there is no plan for systematic treatment of osteosarcoma, it is best not to proceed with a biopsy to avoid potentially accelerating the spread or even hastening metastasis. Therefore, the diagnosis of osteosarcoma must be approached with caution, requiring a combination of clinical symptoms, necessary auxiliary examinations, and pathological analysis.