Abstract
As a consequence of the improvements in diagnostic technology along with gains in life expectancy of cancer patients, the incidence of spine metastases has increased. Spine metastases can affect the patient’s quality of life and negatively impact on their prognosis. Multidisciplinary treatments involve surgery, chemotherapy, radiosurgery and radiotherapy. Spine metastases should be treated using a multidisciplinary and integrated approach that involves spinal surgeons, medical oncologists and radiologists. More research is required to elucidate the pathological mechanisms involved in the aetiology of spine metastasis. This review describes the current situation regarding the diagnosis of spine metastasis, what is understood about the pathological development of spine metastasis and the evolution of the multidisciplinary treatments that are available for patients with spine metastases.
Introduction
Approximately 20–50% of patients with cancer have spine metastases. 1 Spine metastases are common in many different types of cancer, but are particularly common in patients with lung cancer and breast cancer. 2 The risk of spine metastases increases with age, time since diagnosis and the number of comorbidities present. 2 With the prolongation of the life expectancy of cancer patients and improvements in diagnostic methods, the prevalence of spine metastases has increased concomitantly. 3 Patients with spine metastases usually present with pain, spinal instability and nerve function deficit, all of which can affect their quality of life. 3 This current review will summarize the treatment options for spine metastases in cancer.
Spine metastases in cancer
Cancer cells can metastasize to the spine from a range of cancers including breast cancer,4,5 myeloma,4,6 uterine cervix carcinoma, 7 basal cell carcinoma, 8 peripheral cholangiocarcinoma, 9 follicular thyroid carcinoma, 10 thymic carcinomas 11 and lung cancer. 12 Different tumour types can affect the prognosis of patients with spinal metastases. 13 It has been reported that patients with colon cancer, hormone-refractory prostate cancer, nonsmall-cell lung cancer and hepatocellular carcinoma have a short postoperative survival time if they have spine metastases. 13
The early diagnosis of spine metastases is important to improve prognosis and preserve nerve function. 14 Spine metastases can be detected by computed tomography (CT),15,16 magnetic resonance imaging (MRI),16,17 2-deoxy-2-F-18 fluoro-D-glucose (FDG) imaging, 18 FDG positron emission tomography (PET), 19 technetium-99m bone scintigraphy 20 and F-18 fluoromethylcholine PET CT. 21 MRI combined with perfusion parameters can predict local control after stereotactic body radiation therapy (SBRT) in sarcoma spine metastases. 22
Mechanisms of spine metastases in cancer
The processes involved in the establishment of spine metastases include transportation from the primary tumour, arrest within the spine and growth of cancer cells. 3 Cancer cells need to pass through the pre-existing cells and stroma within the primary tumour, detaching from these cells and stroma by reducing their levels of cell surface adhesion molecules and opening the epithelial basal lamina, in order to reach and penetrate the blood vessels that will facilitate their transportation around the body. 23 The tumour cells also need to escape the defence mechanisms of the immune system. 23 If these mechanisms are successful, then the primary cancer cells can metastasize to the spine where they grow within the bone marrow. 23 The venous, arterial and lymphatic systems are the principal routes used to facilitate the metastatic colonization of the spine.8,12 Invasion of cancer cells in the bone stimulates the production of growth factors, which can active the osteoblastic or osteolytic processes. 23 Many molecules are involved in osteoblastic and osteolytic processes, including matrix metalloproteinases, proteoglycans, interleukin-1, transforming growth factor-β and vascular endothelial growth factor, 12 but there is limited information on the specific mechanisms involved in the development of metastases in the spine. Further research into the mechanisms involved in spinal metastases is urgently required.
Treatment evolution of spine metastases
From the 1970s, physicians tried to treat spine metastases using a Halo cast, 24 a Halo vest and radiotherapy 25 and surgery.4,5,26–29 Currently, a multidisciplinary approach is the most common treatment strategy for spine metastases, which usually includes surgery,29–36 radiotherapy,15,37–48 bone cement,49,50 bisphosphonates 51 and chemotherapy. 51 Radiotherapy is an efficient therapeutic approach for symptomatic spine metastases patients that has a low morbidity rate.41,52–56 Surgery remains the standard treatment for patients with rapidly progressive spinal cord compression or patients with a high risk of fracture, but it can cause postoperative complications and delay the initiation of other anticancer therapies.28,31,57 Minimally-invasive techniques can improve spine stabilization and reduce the morbidity of spine metastases.1,30,34,58–64 It is clear that there are several treatments available for spine metastases but not every method is suitable for every patient. The different methodologies have their own characteristics, offering both advantages and disadvantages according to the clinical situation (Table 1). The subsequent sections of this review will summarize the advantages, limitations and some indications of the different treatment modalities that are currently available for spine metastases.
Treatment options for spine metastases.
External stabilization is a choice for spine metastasis. With the assistance of orthoses, biomechanical stabilization can be achieved at different spinal levels. However, it can cause some skin complications and may not provide sufficient pain relief in spine metastasis. Thus, it is mainly used in those patients who are awaiting surgery or those that cannot have surgery. 63
Radiotherapy is also a common therapeutic approach for cancer patients with spine metastasis. Conventional external beam radiation can provide some palliative effects, 42 but this conventional method uses a two-dimensional technique and has a large margin. This increases the risk of unnecessary irradiation to the adjacent normal tissues, so in order to limit the risk of toxicity the radiation is given in fractionated doses, but this can be extremely inconvenient to patients.55,65 To improve radiation therapy, three-dimensional conformal radiation therapy was developed. 55 This technique is based on CT simulation, so there is a better dose-volume calculation that reduces unnecessary irradiation to adjacent organs and provides a more homogeneous irradiation of the target tumour, but the dosage can still not be high enough even with this technique. 55 With the advancement of radiation therapy technology, radiosurgery that can provide pain relief and improve neurological function has been developed. For example, stereotactic radiosurgery with the help of an image-guidance system can provide a precise high dosage of radiation on the target vertebra while sparing the neighbouring vertebrae and normal tissue especially the spinal cord. 42 Even in some radio-resistant tumours, stereotactic radiosurgery can be more efficient than external beam radiation. 54 In the treatment of relapsed vertebral metastasis, external beam radiation only can deliver a modest dose due to the need to avoid radiation-induced injury, but image-guided intensity-modulated radiotherapy can deliver a higher dose of radiation that can better control the recurrent tumour. 43 Compared with conventional external beam radiation, stereotactic radiosurgery can preserve more bone marrow, which can be important for the tolerance of chemotherapy. 52 Moreover, stereotactic radiosurgery is given in one session, which is convenient for patients and does not disturb any ongoing chemotherapy. 52 Furthermore, it had been demonstrated that single-session stereotactic radiosurgery can provide a higher rate of long-term pain control than multisession stereotactic radiosurgery, but multisession stereotactic radiosurgery provides better local tumour control. 42 It should be noted that radiosurgery cannot solve all the problems and it has its own associated complications. For example, if the pain is caused by the loss of mechanical stability of the spine, radiotherapy is unlikely to relieve that because it lacks the ability to stabilize the spine. 63 In addition, radiosurgery is associated with the risk of vertebral compression fractures. Stereotactic body radiotherapy, a type of stereotactic radiosurgery, is associated with a crude risk rate of vertebral compression fracture of 14%. 66 Baseline compression fracture, lytic tumour and misalignment are risk factors for stereotactic body radiotherapy-induced vertebral compression fracture. 66
Surgery is another common choice for spine metastasis treatment. Surgery for patients mainly aims to restore spine stability, relieve pain, decompress the spinal cord and retrieve tissue samples for pathological diagnosis. 57 Indications for open surgery are severe pain or significant fracture with displacement, rapidly progressing neurological deficits, failure of conservative treatment, necessary pathological diagnosis, relatively long life expectancy and a relatively good general condition.28,51 The surgical approaches and reconstructions that can be used are various and determination of which to use depends on the location of the tumour, the infiltration of the tumour, experience of the surgeons and general condition of the patients. 51 For reconstruction surgery, a new radiolucent system has been developed that can effectively restore the stability of the spine without causing any disturbance to CT, MRI and radiotherapy when compared with a traditional metal system. 27 However, most patients with spine metastases are at a late stage of the disease with many comorbidities, malnutrition and poor immune status. Open surgery can cause considerable damage to muscles, blood loss during surgery and it is associated with a high risk of postoperative infections. Patients may not be able to tolerate open surgery. Thus, minimally invasive approaches have been developed and offer several advantages. For example, corpectomy that is used to treat thoracic spine metastasis can be applied through video-assisted thoracic surgery (VATS). 30 VATS can limit the damage to soft tissue and provide a good field of vision for surgeons. 30 The VATS approach is not indicated in patients that cannot tolerate single lung ventilation or have severe pleural adhesions. 30 Another minimally invasive approach, which uses expandable working tubes and percutaneous pedicle screws, was reported to provide stabilization and decompression for treating thoracolumbar spine metastasis. 34 This method can relieve pain and improve neurological function whilst causing less injury and having a lower complication rate. 34 Moreover, patients can start adjuvant therapies earlier after surgery. 34 But this approach is only indicated in patients with anterior compression that is limited to one level and in those without kyphosis that needs anterior column reconstruction. 34 Percutaneous vertebroplasty, percutaneous kyphoplasty and percutaneous osteosynthesis are also minimally invasive surgical options for spine metastasis. 63 Percutaneous vertebroplasty is indicated in patients that do not tolerate surgery or radiotherapy. 63 It can relieve pain and enhance the strength of the vertebrae, but it has contradictions such as spinal cord compression, tumour extension to the posterior wall of the vertebra, vertebral collapse of more than 75% and recent fracture. 63 The use of percutaneous vertebroplasty in cervical metastasis treatment through the anterolateral approach is not indicated in extremely overweight patients and in patients that find it difficult to maintain a cervical extended position. 62 Cement leakage, spinal cord or radicular compression and pulmonary embolism are potential complications. 63 Percutaneous kyphoplasty is a variant of percutaneous vertebroplasty in which kyphon balloons are used to restore the height of the vertebra.63,67 The risk of cement leakage is lower than with percutaneous vertebroplasty and it allows the treatment of collapsed vertebra. 67 Its absolute contradiction is spinal cord compression. Posterior wall involvement is a relative contradiction. However, because of restriction of the size of the balloon, this approach is not suitable for cervical lesions.63,67 The vertebral stenting system also provides an effective treatment strategy for spine metastasis. For example, compared with single kyphoplasty, vertebral stenting can improve osteointegration of the cement into the vertebral body, decrease the dose of cement used as well reducing the risk of cement leakage. 68 If posterior elements are affected or the tumour has infiltrated the spinal canal, the former two approaches will be not sufficient and patients will need extra instruments to restore spinal stability. Percutaneous osteosynthesis will have some difficulties in patients with osteoporosis. 63 In addition to improvements in surgical techniques, there have also been advancements in how materials are injected. Radioactive isotopes such as samarium-153 can be mixed into bone cement so that minimally-invasive surgery can be combined with radiation therapy. This strategy enhances the antitumour activity of the cement implant, and due to the characteristics of the emitted β radiation, the radiation can be limited to within a small local region.49,69,70 This will cause less radiotherapy-induced toxicity than the parenteral application of strontium-89. 71 The advantages and disadvantages of various treatments are summarized in Table 2.
Advantages and disadvantages of using radiotherapy for the treatment of spine metastasis.
In conclusion, spine metastases should be treated using a multidisciplinary and integrated approach that involves spinal surgeons, medical oncologists and radiologists. More research is required to elucidate the pathological mechanisms involved in the aetiology of spine metastases.
Footnotes
Declaration of conflicting interest
The authors declare that there are no conflicts of interest.
Funding
This study was supported in part by grants from the following organizations: National Natural Science Foundation of China (no. 81802255), Shanghai Pujiang Programme (no. 17PJD036), Shanghai Municipal Commission of Health and Family Planning Programme (no. 20174Y0131), National Key Research & Development Project (no. 2016YFC0902300), Major Disease Clinical Skills Enhancement Programme of three year action plan for promoting clinical skills and clinical innovation in municipal hospitals, Shanghai Shen Kang Hospital Development Centre Clinical Research Plan of SHDC (no. 16CR1001A), ‘Dream Tutor Outstanding Young Talents Programme’ (no. fkyq1901), Key Disciplines of Shanghai Pulmonary Hospital (no. 2017ZZ02012) and Shanghai Science and Technology Commission (no. 16JC1405900) Leading Talents in 2014.
