Bone is the most common site of metastasis for malignant tumors other than lung and liver. About 70% to 80% of cancer patients will eventually develop bone metastasis, and its incidence is about 35-40 times that of primary malignant bone tumors, which is a frequent problem encountered by orthopedic surgeons. When patients with a history of primary malignancy present with bone destruction, the possibility of bone metastases should be highly suspected, but in 22.6%-30.0% of cases lacking a history of malignancy, patients with metastases of unknown origin should be diagnosed with a primary tumor. The results of a prospective study on diagnostic strategy showed that the primary tumor could be found in about 85% of cases after standardized diagnosis. And the standardized diagnosis should include:1. Patient age, medical history and site of onset:In cases over 40 years of age, the incidence of bone metastases is much higher than that of primary bone tumors. Bone metastases are usually located in the proximal end of the extremity bones or in the spine. Most bone metastases of unknown origin are from the lungs or kidneys, so most primary tumors can be detected by examination of the thoracic and abdominal organs.2. Physical examination: The focus should be on the prostate, breast, thyroid and abdomen, which are likely to yield more hints.3. Laboratory tests: It is generally difficult to determine the source of tumors by laboratory tests (except PSA and AFP), but they can be used to exclude multiple Myeloma. 4. Imaging evaluation: The examination sites mainly focus on the thoracic and abdominal organs, and the examination methods mainly include X-ray, ultrasound and CT. Bone scan and PET can also be performed for the diagnosis of bone metastases.5. Pathological diagnosis: In addition to the above tests, pathological examination is often needed to clarify the diagnosis, and in combination with immunohistochemistry, more information on the primary tumor can be obtained. Combination with other clinical examinations can distinguish the origin of tumor cells in up to 72% of cases. Principles and indications of preoperative puncture biopsy: 1. Preoperative biopsy must be performed in patients with no history of tumor but suspected bone metastases. 2. If the history of malignant tumor is clear and multiple bone destruction (long bone, vertebrae, pelvis) is found throughout the body at the same time, preoperative biopsy is not a mandatory operation. 3. For patients with a clear history of malignancy but only single bone destruction, biopsy should be considered to clarify the diagnosis before planning surgery. The literature reports that about 15% of new bone lesions in patients with long-term surviving malignancies may be other new tumors or non-tumor lesion projections.