Bone is a good site for distant metastasis of cancer. When malignant tumor cells metastasize to bone tissue, it causes bone destruction and a series of symptoms, and finally leads to a serious decline in the patient’s quality of life. At present, a lot of progress has been made in the research on the characteristics, mechanisms of occurrence, diagnosis and treatment of bone metastases. This article is a review of the relevant studies.
I. Clinical characteristics
With the increase of treatment efficacy and survival of primary malignant tumors, the frequency of bone metastases in clinical practice is also increasing. Conroy reported 429 cases of metastatic bone tumors in which the primary tumors were breast cancer (32.6%), lung cancer (22.1%), and prostate cancer (7.7%) in order of origin.
In men, prostate cancer was the most common (60%), while in women, breast cancer was the most common (70%), followed by lung, kidney, thyroid and digestive system. The distribution of primary foci of bone metastases in 3270 cases of malignant tumors in China in recent years were: 1052 cases of lung cancer (32.2%), 787 cases of breast cancer (24.2%), 323 cases of unknown site (9.9%), 171 cases of nasopharyngeal cancer (5.2%), 137 cases of colorectal cancer (4.3%), 127 cases of gastric cancer (3.9%), 99 cases of prostate cancer ( 3.0%), 98 cases of esophageal cancer (2.9%), 53 cases of cervical cancer (1.6%), 47 cases of thyroid cancer (1.4%), 41 cases of kidney cancer (1.3%), 24 cases of other gastrointestinal cancers (0.73%), 23 cases of soft tissue sarcoma (0.70%), 19 cases of ovarian cancer (0.58%), and 14 cases of pancreatic cancer (0.43%).
Clain A analyzed 2000 patients who died of bone metastases and the sites involved were as follows: 69% of the spine, 41% of the pelvis, 25% of the femur and 14% of the skull, and the upper limb bones were less frequently involved, accounting for about 10-15%. The upper limb bones were less frequently involved, accounting for 10%-15%. Zhang Xintao analyzed the results and found that spinal metastases were the most common, accounting for 37.7%, with thoracic and lumbar spine involvement, pelvis accounting for 12.5%, ribs accounting for 10.8%, and femur accounting for 10.4%. Multiple metastases throughout the body account for 15.4%, mostly in the advanced stage of tumor. Cancer bone metastases can be divided into three types: osteolytic, osteogenic and mixed types. The results of analysis of 325 cases by Zhang Xintao et al. showed that osteolytic destruction accounted for 82.1%, osteogenic changes accounted for 10.6% and mixed type accounted for 8.3%.
II. Pathogenesis
The seed-and-soil theory has been widely accepted on the targeting of malignant tumors to bone tissue. The mechanisms of metastasis currently studied include two aspects.
(1) the biological characteristics inherent to tumor cells themselves, i.e., tumor cells have the ability to migrate away from the primary site to skeletal tissues. The phenomenon that malignant tumors become more and more aggressive during growth is called tumor evolution, including accelerated growth, infiltration of surrounding tissues and distant metastasis, which is related to tumor heterogeneity.
During the growth of monoclonal tumors, there are additional genetic mutations that cause subclones of tumor cells to acquire different characteristics, as a result of which not all tumor cells in the tumor cell population have metastatic properties, and metastasis is caused by some of these tumor cells with metastatic ability. For example, breast cancer, lung cancer, prostate cancer, kidney cancer and thyroid cancer are most prone to bone metastasis, which are called osteophilic tumors, while skin cancer, oral cancer, esophageal cancer and colon cancer rarely have bone metastasis, which are called osteopathic cancers.
(2) The anatomical characteristics of specific parts of the skeletal system and the biological characteristics of bones are also related to bone metastasis. In adults, the red bone marrow of the limbs is gradually replaced by yellow bone marrow, while the spine, pelvis, femur and proximal humerus are still red bone marrow, which are rich in blood transport and contain a large number of blood sinuses, so tumor cells can enter and stay in the bone marrow tissue without any obstruction;
On the other hand, the spinal venous system is located in the dura mater and around the spine, without venous valves, with traffic branches connected to the superior and inferior vena cava. Therefore, when tumor cells enter the blood circulation, they can cross the liver and lungs to the spine and pelvis to form metastatic tumors. The same pathophysiological defect exists in the iliofemoral venous system.
Lung cancer cells can enter the pulmonary vein and reach the bone through the arterial system. Tumor cells that enter the lung from the vena cava can sometimes enter the bone from the arterial system without stopping; metastasis through the lymphatic vessels is rare, but breast cancer can spread from the axillary lymphatic vessels to the proximal humerus. In addition, the fragments of type 1 collagen and osteocalcin that appear during the renewal process of normal bone tissue have a chemotactic effect on the metastatic tumor cells.
Osteolytic metastasis is mainly associated with bone resorption by osteoclasts, which accelerates bone catabolism and produces osteolytic lesions due to the enhanced activity of osteoclasts. The most important regulator is parathyroid hormone-related protein (PTHrP). Tumor cells metastasizing to bone tissue specifically express PTHrP, and breast cancer cells metastasizing in osteolytic bone metastatic lesions highly express PTHrP. Animal tests have confirmed that PTHrP is associated with multiple osteolytic metastases, strongly suggesting that PTHrP is closely associated with tumor bone metastasis and osteolysis.
Another critical factor is the cytokine κB receptor activator ligand (RANKL). Signaling by RANKL is essential for osteoclast differentiation, activation and survival, and a variety of tumor cells can produce excess RANKL, leading to osteoclast activation and bone tissue lysis. Bone metastases from certain tumors exhibit osteogenic changes mediated by factors that contribute to osteoblast growth and differentiation.
Prostate cancer cells produce large amounts of TGF-β, which is a strong stimulator of bone formation, and prostate cancer cells also secrete fibroblast growth factor (FGF), which stimulates the proliferation of osteoblasts and bone formation. Patients with prostate cancer bone metastases have significantly higher plasma levels of endothelin, a regulator of osteogenic metastasis, which mediates the osteogenic response by activating alkaline phosphatase.
Many studies have confirmed that integrin expression is upregulated on the surface of malignant tumor cells, and their metastatic ability is positively correlated with integrin expression levels. Integrin ligands are expressed at high levels in tissues where tumors are prone to metastasis. Bone tissue expresses laminin, type I collagen, OPN and fibronectin in high amounts, and integrins specifically bind to these molecules, contributing to the metastasis of tumor cells to bone tissue.
The expression of CD44, a hyaluronan receptor, binds to hyaluronic acid, collagen, chondroitin sulfate, and laminin to mediate the adhesion of tumor cells to bone tissue. CD44 is a hyaluronan receptor that binds to hyaluronic acid, collagen, chondroitin sulfate, and laminin and mediates the development of adhesion.
The expression of CD44 molecules on the surface of bone marrow vascular epithelial cells predisposes myeloma to homing to bone tissue. The tissue specificity of tumor cell metastasis and the specific adhesion of malignant tumor cells to the vascular endothelium are related. Prostate cancer cell lines with strong bone metastasis were found to have enhanced adhesion specifically to bone marrow vascular endothelial cells. Tumor cells require the participation of several enzymes in breaking through the basement membrane, including serine proteases, cysteamine proteases, aspartate proteases, matrix metalloproteinases (MMPs), and most importantly, the matrix metalloproteinase system.
Bone tissue and tumor cells metastasizing to bone tissue highly express urokinase-type fibrinogen activator (Upa), and Upa activates matrix metalloproteinases. Prostate cancer cells express high amounts of MMP, which is able to degrade type 1 collagen in bone tissue, and this is one of the important reasons why prostate cancer metastasizes easily to bone tissue. The ECM of bone tissue contains a large number of growth factors, including transforming growth factor beta (TGF-β), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF), fibroblast growth factor (FGF), and bone morphogenetic protein (BMP).
These growth factors promote the growth and invasion of tumor cells metastasized to bone tissue; TGF-B promotes the growth and differentiation of a variety of cells, FGF stimulates the growth of prostate cancer cells, and PDGF promotes cytokinesis. Moreover, these growth factors can upregulate the expression of integrins on the surface of tumor cells and enhance the invasion and multiplication of tumor cells.
III. Diagnosis
The diagnosis of bone metastases includes the diagnosis of the primary tumor and the diagnosis of metastatic lesions. Some tumors have metastatic lesions as the first manifestation and are dominated by the manifestation of metastatic lesions, and about 10% of bone metastases cannot find the primary lesions. Pain is the main complaint of most patients. 53.3% of patients visited the clinic for bone pain as reported by Tony Xu. 21.5% of patients visited the clinic for symptoms of primary foci, and bone metastases were found during physical examination. 2.1% of patients visited the clinic only because of paraplegia due to spinal cord compression. Pathologic fractures account for 10.3% of cases, sometimes without clinical symptoms, and are diagnosed only from imaging.
1. Biochemical test indicators
The biochemical indicators of bone resorption include urinary pyridinol (uPYD) and urinary deoxypyridinol (uDPD), and the biochemical indicators of bone formation include serum bone-specific alkaline phosphatase (sBAP) and serum osteocalcin (sBGP). The results of Marchei et al. showed that the concentration levels of uPYD/Cr, uDPD/Cr and sBAP were significantly higher in patients with osteolytic metastases of malignant tumors, and Yu Jing’s study in China found that the bone metastasis of progressive tumors (+) group was higher than that of the tumor-limited group and the bone metastasis of progressive tumors (-) group. The levels of uPYD/Cr, uDPD/Cr, and sBAP were significantly higher in the stage tumor bone metastasis (-) group than in the stage tumor bone metastasis (-) group, suggesting that the concentration levels of uPYD, uDPD, and sBAP may play a role in monitoring and evaluating malignant tumor bone metastasis.
In recent years, it has been found that type I collagen is the only collagen in bone tissue, accounting for 90% of the bone matrix. Type I collagen cross-linked amino-terminal peptide (NTx) and type I collagen cross-linked carboxy-terminal peptide (ICTP) are their specific products, which only originate from the destroyed mature bone matrix and are no longer further broken down, NTx and ICTP can therefore be used as indicators of osteolytic bone metabolism. 70-80% of patients with metastatic bone tumors have serum amino-terminal product and carboxy-terminal product concentrations that are 2-7 times higher than those of healthy controls. Their total concentrations correlated with the risk of metastatic bone tumors. costa et al. concluded that changes in urinary amino-terminal products were sensitive and specific as predictors of tumor bone metastases, were not increased in patients with only extraskeletal metastases, and were better predictors of metastatic bone tumors than bone-specific alkaline phosphatase, type 1 collagen carboxy-terminal peptide, and CA-153.
Horiguchi et al. reported that type I collagen cross-linked carboxy-terminal peptide (ICTP) assay was a very good diagnostic method for confirming bone metastases, with sensitivity, specificity and accuracy of 92.0%, 70.0% and 81.6%, respectively. Lv Xiaofang’s study found that blood ICTP may precede the detection of bone metastases by imaging. Urine NTx and blood ICTP are important references for the diagnosis of bone metastases in patients with malignant tumors and can assist in the timely diagnosis of malignant tumor bone metastases. There are also anti-tartaric acid type phosphatase (TRAP) isoform 5b, bone bridge protein and nuclear factor κB receptor activator ligand (RANKL), etc. TRAP isoform 5b is meaningful for the early diagnosis of bone metastases, determination of severity and evaluation of treatment effect. RANKL acts on its receptor, thereby activating osteoclasts and inducing osteoclast precursor differentiation.
2. Imaging examination
(1) X-ray examination.
X-ray examination can identify osteolytic and osteogenic damage and detect certain pathological fractures, but its specificity is high and sensitivity is low. Positive results can only be obtained when the trabecular structure is more than 50% destroyed and the lesion is more than 1.0-1.5 cm in diameter. In addition, metastases often invade the bone marrow first, and the high density of the bone cortex tends to conceal the potential destruction; in elderly patients, the cancellous bone destruction caused by metastases is difficult to show due to osteoporosis, so some bone metastases can be shown only after 18 months of ECT abnormalities. Cao Laibin’s analysis found that X-ray sensitivity was 48.1%, while metastases occurring in cortical bone could be detected earlier.
X-rays are not routinely used for further evaluation of abnormalities found in areas with clinical symptoms (e.g., pain, pathological fractures) or other imaging studies (e.g., whole-body bone imaging and MRI). x-rays mainly show worm-like bone destruction, which can be multifocal or fused into a sheet, with little periosteal and soft tissue reaction. Osteogenic bone metastases may appear as cottony, dentin-like, or glassy densities.
The specificity of X-rays is high, 94.4% compared to 66.7% for ECT, and certain features of bone metastases on X-rays are useful in differentiating them from other lesions or primary bone tumors. X-rays can be used to assess the risk of pathologic fracture of the affected area. If there is 30% or more localized cortical destruction, the risk of pathological fracture is increased and appropriate treatment is required.
(2) CT examination.
CT is more valuable for patients with positive systemic bone imaging and negative radiographs, with local symptoms and suspected bone metastases. CT scans are more sensitive than radiographs in detecting bone metastases and can show infiltrative bone destruction and soft tissue masses, while enhanced scans can clearly show the vascular-rich nature of bone metastases and the relationship between the lesion and surrounding nerve and vascular structures.
CT can help detect metastases in the spine that are protruding into the spinal canal and compressing the dural sac and nerve roots. CT can also detect destruction of the spinal canal wall and whether the tumor tissue is protruding into the spinal canal to compress the dural sac and nerve roots. Because the normal fatty tissue in the bone marrow cavity is replaced by tumor tissue, the density in the affected marrow cavity is increased. CT can detect metastases that are confined to the marrow cavity at an early stage and have not yet shown significant bone destruction, and CT examinations can help to detect the primary tumor foci. In addition, CT-guided aspiration biopsy can be performed on the lesion, thus improving the rate of early pathological diagnosis.
(3) MRI examination.
MRI has high sensitivity for early metastases that exist only in the bone marrow cavity, and can accurately show the invasion site, scope and surrounding soft tissues, and can be used for multiplanar imaging, which can help to explore other metastases that are easier to perform puncture biopsy. Most of the bone metastases are hematologically implanted in the bone marrow, and MRI is most sensitive to show early bone metastases because a significant number of tumor cells can already exist in the bone marrow before the whole-body bone imaging shows abnormal local radiological uptake.
Gd-DTPA-enhanced MRI can show more metastases, which can help to make more accurate staging and prognosis of tumor patients. It is generally believed that MRI has higher sensitivity than whole-body bone imaging and can show early bone metastases that cannot be shown by the latter, especially for lesions with spinal metastases.
Some scholars believe that MRI can be a simple and inexpensive means of detecting metastases in the mid-axis bones (spine, pelvis, and proximal femur). MRI should be used as a confirmatory test for positive systemic bone visualization sites. Recently, the sensitivity and specificity of whole-body MRI with fast STIR sequences have been reported to be significantly higher than that of whole-body bone imaging.
(4) Whole-body bone imaging.
Because whole-body bone imaging can evaluate the whole body and provide some functional and hematologic information, whole-body bone imaging has long been the standard and preferred method for detecting bone metastases. 99mTc-MDP is often used as the contrast agent, and its mechanism of showing the lesion is that the radiotracer is adsorbed on the bone surface, and the amount of uptake is related to the local osteogenic activity and blood flow. The increased metabolism and rich blood supply of the affected bone cause a corresponding increase in radioactive uptake (radioactive concentration or “hot zone”), while the decreased metabolism and reduced blood flow result in a lower radioactive uptake (radioactive sparing or “cold zone”).
When the metastases are ≥2 mm in diameter and have altered metabolic function, they can be detected by bone scan. The test has a high sensitivity, and can be detected when there is a 5%-15% change in local bone metabolism, and the detection time is 1-6 months earlier than that of X-ray examination, but there is a considerable false-negative rate for lesions in the spine and confined to the bone marrow. The sensitivity of bone imaging in diagnosing bone metastases was 87.8%, and bone imaging missed mainly some lesions with mainly osteolytic lesions, which were also easily missed because of the thin and small cervical vertebral body. The specificity of bone imaging is low, and trauma, inflammation and osteoarthritis can lead to local concentration of radionuclides, resulting in false positives.
Rybak et al. concluded that only 50% of single foci of concentration in tumor patients are bone metastases. Therefore, a positive whole-body bone image is usually further confirmed by radiographs or CT examinations. If the X-ray is positive, the metastasis can be confirmed, and if the X-ray is negative, the possibility of bone metastases cannot be excluded.
With the development of nuclear medicine technology, the clinical application of single photon emission computed tomography (SPECT) technology has improved the sensitivity and specificity of whole-body bone imaging for the detection of bone metastases to a certain extent. PET in PET/CT can detect bone marrow involvement not yet detected by CT, and CT can accurately localize lesions detected by PET, so PET/CT has higher sensitivity and specificity than PET and CT alone for the diagnosis of malignant and benign bone lesions.
The tomographic imaging technique of SPECT helps to precisely localize the lesions, especially in the complex anatomy of the spine and pelvis, thus improving the sensitivity of detecting metastases occurring in these areas and helping to differentiate them from the abnormalities in the imaging caused by some degenerative joint changes. The false-positive rate of bone metastases diagnosed by bone imaging was reduced. In the analysis of Li Wei et al, the diagnostic compliance rates of whole-body bone imaging, local tomographic bone imaging, CT imaging and SPECT/CT fusion images were 51.7%, 93.1%, 89.7% and 100%, respectively.
Metser et al. concluded that 18F-FDG PET-CT has better specificity than 18F-FDG PET in detecting metastatic bone tumors in the spine, and can precisely localize and identify soft tissue invasion. In the analysis of 35 patients with abnormal bone lesions, Han Lijun et al. found that the sensitivity, specificity and accuracy of PET in diagnosing bone metastases were 91.2%, 81.0% and 88.8%, respectively, while the sensitivity, specificity and accuracy of CT in the same machine were 80.9%, 76.2% and 79.8%, respectively. The sensitivity, specificity and accuracy of PET-CT fusion images for the diagnosis of bone metastases were 94.1%, 90.5% and 93.2%, respectively.
3. Biopsy of bone tumors
Biopsy is the most accurate and reliable diagnostic method, and it is easy to obtain a more satisfactory pathological histological diagnosis because of the accurate site. It is generally believed that the soft tissue infiltrating part shows the highest malignancy of the tumor, while the medullary tumor part tends to be differentiated and beneficial to explore its tissue origin.
Closed biopsy (percutaneous puncture), including both aspiration and coring methods. The former is suitable for tumors with abundant cellular components, bone marrow tumors and metastases. The latter is more favorable for substantial tumors, especially those containing fibers, bone or cartilage, and more tumor tissue can be retrieved.
Incisional biopsy destroys the original barrier, encircling band and soft tissue interstitial compartment of the tumor, causing tumor contamination. If the location of the tumor is more complicated than deep open biopsy, biopsy near the nerve and vascular area has the possibility of bleeding and contamination by the tumor and affects limb preservation, and incorrect incision will increase the difficulty of the next surgery or even lose the chance of limb preservation. Therefore, closed biopsy should be given priority.
IV. Treatment
The presence of bone pain in metastatic bone tumor may be related to the following factors.
1.Tumor cell-mediated chemical irritation or cell infiltration, spreading to the periosteum or spreading to the nerve tissue and causing persistent bone pain.
2. Mechanical compression of tumor causes thinning of bone tissue; in large metastases, the tension of bone cortex increases, causing bone pain.
3. Inflammatory reaction at the site of bone metastasis, inflammatory mediators can activate and sensitize joint sensation, thus causing increased pain.
In the treatment of bone metastases, the following should be understood.
(1) Bone metastasis is a common phenomenon in patients with malignant tumors;
(2) Pain from bone metastases requires immediate treatment;
(3) Patients with simple bone metastases have a longer survival period than those with visceral metastases;
(4) The appearance of symptoms in patients with bone metastases is earlier than that of lung metastases and liver metastases, and the symptoms are also more severe.
(i) Drug treatment
Drug therapy for pain should be individualized and administered on time. The routes of administration include oral, dermal, rectal, continuous subcutaneous, intravenous and intramedullary injections. Antidepressants, corticosteroids and anticonvulsants can be used in combination to enhance pain management. According to the biological characteristics of the primary tumor, different chemotherapy regimens and hormone therapy can be used. For example, for bone metastases from breast cancer, small cell lung cancer, malignant lymphoma, prostate cancer, etc., the use of chemotherapy regimens that are sensitive to the treatment of the primary lesion can also have a therapeutic effect on bone metastases, while the application of endocrine therapy for tumors that are effective in hormone drug treatment, such as breast cancer and prostate cancer, can also be effective on bone metastases. Endocrine therapy can be effective for bone metastases.
Bisphosphonates such as disodium pamidronate and zoledronic acid are powerful inhibitors of osteoclasts, inhibit osteoclast activity and induce apoptosis of osteoclasts, and inhibit the release of pain transmitters from osteoclasts and tumor cells. Sun Hui et al. reported that the application of these drugs for the treatment of pain in bone metastases achieved an efficiency of more than 80%. Hypercalcemia affects 10% to 40% of cancer patients. Common complications of hypercalcemia are anorexia, nausea, vomiting and polyuria, dehydration, and constipation.
Confusion is also a common symptom and can progress to bradykinesia and coma. Bisphosphonate therapy is the mainstay of anti-hypercalcemia treatment and is able to normalize plasma calcium ion concentrations in 70% to 100% of patients with malignant hypercalcemia and is well tolerated. The best treatment for tumor-induced hypercalcemia is effective treatment of the primary malignancy, and due to the lack of effective anticancer therapy, control of hypercalcemia becomes the only option.
(ii) Radioisotope therapy
Radioisotope therapy of bone is to inject a radioactive substance with strong osteophilicity, capable of emitting β-rays with suitable half-life into the body, so that a highly selective radionuclide concentration can appear at the site of bone metastasis, and use the β-rays continuously emitted by this radionuclide to irradiate the metastasis to achieve pain relief and kill tumor cells. The radioisotopes used in clinical applications include 89Sr, SmEDTMP, Re-HEDP, P and so on.
SmEDTMP is not only effective for palliative treatment and analgesia for patients with bone metastases, but also has the effect of tumor regression for some patients. 89Sr uptake in bone metastases is 2-25 times that of normal bone, and its cancer/bone marrow radiation ratio is more than 10. 89Sr has a long physical half-life, and once it is incorporated into metastases, it is no longer metabolized and renewed, just like 89Sr in normal bone, and can remain in metastases for at least 100d. It can remain in the metastasis for at least 100 d, and thus a great part of the radiation effect is achieved during this period, so the efficacy is better.
Clinical applications have confirmed that the analgesic rate of 186Re-HEDP for bone pain in metastatic bone cancer is 70% to 90%, and the analgesic relief rate is more rapid and longer maintained compared with 89Sr in the treatment of bone metastases, with an average response period of 5.7 months. 32P has the properties of phosphate, diphosphate and colloid, which can concentrate in bone marrow, bone trabeculae and bone, and can relieve bone pain caused by bone metastases. Because 32P has obvious inhibitory effect on hematopoietic system, it is less used in clinic nowadays.188Re is a very ideal radionuclide for treating bone pain of tumor bone metastasis, and has a good prospect of clinical application.
(iii) Radiotherapy
Radiotherapy is preferred for the relief of pain at a single site. Local radiotherapy is a very effective method for treating bone metastases, aiming at pain relief, preventing pathological fractures, improving patients’ mobility and functional status, and prolonging patients’ lives. Radiotherapy can be administered at 15Gy/5 irradiations or 40.5Gy/15 irradiations, with an efficiency of about 85%. Pain relief is complete in 50% of patients and partial relief in 35% of patients.
The duration of complete pain relief is 12 to 15 weeks, with a 28% complete relief rate with 25 Gy/5 irradiations. 1998 American College of Radiology Expert Panel on Radiotherapy of Bone Metastases recommended the following dose fractions: 20 Gy/5, 30 Gy/10, or 35 Gy/14. The choice of optimal dose fractionation is independent of the pathological type of the primary tumor, the disease-free interval before the appearance of bone metastases, and the number of metastases, with a rapid treatment regimen chosen for patients with short survival (less than 3 months).
The results of the Bone Pain Trial Working Party study in the UK showed no significant differences between the two groups in terms of survival, pain relief and pain medication application between 8GY primary irradiation and multiple split irradiation (20GY/5 times, 30GY/10 times). However, a single 8GY irradiation was more convenient for patients and less expensive. In clinical practice, most hospitals in China often choose 20 Gy in 5 irradiations over 1 week or 30 Gy in 10 irradiations over 2 weeks, and pain relief occurs quickly, with more than half of the patients feeling effective in 1 to 2 weeks.
Re-treatment may not be as effective as the first treatment, but significant pain relief can still be obtained. When external irradiation is considered to be more dangerous, treatment with radioisotopes is a better option for symptom relief.
(iv) Surgical treatment
Surgery has a certain place in the comprehensive treatment of bone metastases, especially in cases where bone metastases cause pathological fractures and spinal cord compression. Before surgery, we should understand some factors affecting patients’ prognosis, such as the malignant degree and biological behavior of the primary tumor; whether the primary tumor is eradicated, and the degree of sensitivity to radiotherapy and chemotherapy; the location of metastases, the number of metastases, and the presence of metastases in other organs; the changes in imaging, such as osteolytic destruction and unclear boundary on X-ray, which indicates poor prognosis of the tumor; if the tumor has clear margins and sclerotic bands, which indicates slow progression of the tumor and poor prognosis. If the tumor margin is clear and there is sclerotic zone, it means the tumor progresses slowly and the prognosis is relatively good. Only when the above conditions are clinically understood can we make a comprehensive judgment on metastatic tumor patients and choose the appropriate surgical treatment plan.
(V) Interventional treatment
Bone cement is injected into the metastatic bone tumor to play a supportive role and has the effect of pain control and tumor containment, especially for vertebral bone, which can prevent the compression of spinal cord and nerve roots after tumor bone destruction. Domestic authors Deng Gang and Wang Zhentang reported an overall efficiency of over 90%.