What are the diagnostic methods for bone metastasis of malignant tumors?

Once a tumor patient develops clinical manifestations such as bone pain, pathological fractures, elevated alkaline phosphatase, spinal cord compression or spinal nerve root compression, or hypercalcemia-related symptoms, further examination should be performed to exclude bone metastasis. What are the diagnostic methods for determining bone metastasis of malignant tumors?

(1) Radionuclide whole body bone imaging (ECT) diagnosis: ECT, also known as "bone scan", is one of the diagnostic methods for bone metastasis of malignant tumors, but it is not used as a basis for the diagnosis of metastatic bone tumors. The sensitivity of radionuclide bone imaging in diagnosing bone metastasis of malignant tumors is 62%-98%, with a false negative rate of 3%-8%; the specificity is 66.7%-70%, with a false positive rate of 33%-40%.

(2) X-ray examination: X-ray examination is also a diagnostic method for bone metastasis of malignant tumors. However, the sensitivity of X-ray examination in early diagnosis of bone metastasis is low, only 44%-50%. Only when the degree of destruction of trabeculae reaches more than 50% and the diameter reaches 1.0cm-1.5cm, can bone metastases visible on X-rays be formed. Although X-ray examination is used for diagnosis of bone metastasis, it has high image spatial resolution, wide application range, simple operation, low price and relatively low radiation. Therefore, X-ray examination is still one of the main examination methods for diagnosing bone metastasis of malignant tumors.

(3) CT scan diagnosis: CT scan is also a diagnostic method for bone metastasis of malignant tumors, and its diagnostic sensitivity is higher than that of X-ray film diagnosis. CT scan examination can confirm bone metastasis lesions in patients with positive radionuclide bone imaging examinations but negative X-ray examinations. For lesions that require bone biopsy, puncture biopsy at the lesion under CT guidance can improve the puncture biopsy rate and location accuracy of bone metastasis lesions and the safety of the operation.

(4) MR scanning (i.e., nuclear magnetic resonance scanning): MR scanning is currently a diagnostic method with high sensitivity and specificity for diagnosing bone metastasis. The sensitivity of MR scanning for diagnosing bone metastasis is 82%-100%, and the specificity is 73%-100%. MR scanning has a special advantage in sensitively showing early metastatic lesions in the bone marrow cavity. MR scanning can also accurately show the site and range of bone metastasis invasion and the involvement of surrounding soft tissues. However, since bone destruction is a reliable indicator for the diagnosis of bone metastasis by imaging examinations, MR examination is not the most reliable method for determining bone destruction. Therefore, there is still controversy over the use of MR for the diagnosis of bone metastasis.

(5) PET-CT scan examination and diagnosis: PET-CT scanning is a new imaging technology that combines positron emission tomography with electronic computer tomography. Both PET images and CT images can be obtained in one imaging. PET imaging detects changes in local glucose metabolic activity to detect tumor lesions. Therefore, PET-CT can more sensitively display bone marrow micrometastasis and diagnose bone metastasis at an early stage. PET-CT scanning can also simultaneously examine systemic organs, lymph nodes and soft tissues to comprehensively evaluate the scope of tumor lesions. The sensitivity of PET-CT diagnosis is 62-100%, and the specificity is 96-100%. PET-CT scanning has special advantages in the diagnosis of bone metastasis of malignant tumors and the comprehensive evaluation of tumor conditions, but due to the high cost of the examination, it is not recommended as a routine examination method.

(6) Bone biopsy diagnosis: Histopathology or cytopathology is a reliable method for confirming bone metastasis of malignant tumors. For suspected bone metastases, fine needle aspiration cytology or puncture biopsy can be performed to confirm the diagnosis.

(7) Examination and diagnosis of bone metabolism biochemical indicators: Bone metabolism biochemical indicators are a new method explored in recent years for the diagnosis of bone metastasis and disease monitoring. Biochemical indicators reflecting osteolytic bone metabolism include: type I collagen C-terminal peptide (ICTP), type I collagen N-terminal peptide (NTX), type I collagen C-terminal peptide (CTX), bone sialoglycoprotein (BSP), etc. Biochemical indicators reflecting osteoblastic bone metabolism include: bone-specific alkaline phosphatase (BALP), total alkaline phosphatase (ALP), type I procollagen N-terminal propeptide (PINP), etc.

Studies have shown that bone metabolism markers such as urinary NTX have certain application prospects in the diagnosis and disease monitoring of bone metastasis of malignant tumors, but currently such indicators cannot be used as a reliable method for the diagnosis of bone metastasis.

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