Erosive bone destruction is defined as a malignant bone tumor with no definite boundary of destruction, no sclerotic ring envelope, and gradual migration between the tumor and normal bone. Eroding bone destruction is caused by malignant bone tumors and is also seen in bone infections. ECT is also called “bone scan”, which is one of the diagnostic methods of malignant tumor bone metastasis, but it is not used as a basis for the diagnosis of metastatic bone tumor. The sensitivity of radionuclide bone imaging in diagnosing bone metastasis of malignant tumor is 62%-98%, and the false negative rate is 3%-8%; the specificity is 66.7%-70%, and the false positive rate is 33%-40%. (2) Diagnosis by X-ray plain film examination: X-ray plain film examination is also a diagnostic method for bone metastasis of malignant tumor. However, the sensitivity of X-ray plain film in early diagnosis of bone metastases is low, only 44%-50%. Only when the destruction of bone trabeculae reaches more than 50% and the diameter reaches 1.0cm-1.5cm, the bone metastases visible on X-ray radiographs may be formed. However, because of the high spatial resolution of X-ray examination, wide application, easy operation, low price and relatively low radiation, X-ray examination is still one of the main examination methods for the diagnosis of malignant tumor bone metastasis. （CT scan is also a diagnostic method for bone metastases of malignant tumors, and its diagnostic sensitivity is higher than that of X-ray plain radiographs. For lesions requiring bone biopsy, CT-guided aspiration biopsy of the lesion can improve the rate of aspiration biopsy of bone metastases and the accuracy of the site and the safety of the operation. (4) MR scan (i.e. MR scan): MR scan is currently a diagnostic method with high sensitivity and specificity for the diagnosis of bone metastases. MR scan can also accurately show the site and extent of bone metastasis invasion and the surrounding soft tissue involvement. However, since a reliable indicator for confirming bone metastases by imaging is bone destruction, MR examination is not the most reliable method for determining bone destruction. Therefore, there is still controversy about the use of MR for the confirmation of bone metastasis. (5) PET-CT scan: PET-CT scan is a new imaging technology combining positron emission computed tomography and electronic computerized body camera, which can obtain both PET and CT images in one imaging. PET-CT scan can also examine the whole body organs, lymph nodes and soft tissues at the same time to comprehensively assess the extent of tumor lesions. 62-100% sensitivity and 96-100% specificity of PET-CT diagnosis. PET-CT scan has special advantages in the diagnosis of malignant tumor bone metastasis and comprehensive assessment of tumor condition, but it is not recommended as a routine examination method because of the high cost of the examination. (6) Diagnosis by bone biopsy: Histopathological or cytopathological examination is a reliable method to confirm the diagnosis of malignant tumor bone metastasis. For suspected bone metastases, fine needle aspiration cytology or aspiration biopsy can be performed to clarify the diagnosis. (7) Diagnosis of bone metabolism biochemical index: Bone metabolism biochemical index is a new method explored in recent years for the diagnosis of bone metastasis and disease monitoring. The biochemical indexes reflecting osteolytic bone metabolism include: type I collagen carbon terminal peptide (ICTP), type I collagen nitrogen terminal peptide (NTX), type I collagen carbon terminal peptide (CTX), bone sialic acid glycoprotein (BSP), etc. The biochemical indicators of osteogenic bone metabolism include bone specific alkaline phosphatase (BALP), total alkaline phosphatase (ALP), pre-collagen type I nitrogen-terminal peptide (PINP), etc.