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Background: Metastatic spinal cord compression (MSCC) is a serious complication of cancer leading to demyelination and axonal damage of the spinal cord with a risk of para/tetraplegia. It is most common in patients with known cancer but may also be the initial manifestation of malignancy (IMM). Patients with MSCC as the IMM have rarely been studied as a separate group. The interaction between the tumour and bone in spinal bone metastasis interferes with regulatory mechanisms, causing the formation of less mechanically competent bone and increasing the risk of spinal instability and fracture. The Spinal Instability Neoplastic Score (SINS) has been proposed as a tool in order to help clinicians evaluate tumour-related spinal instability. The SINS has shown excellent inter- and intraobserver reliability, but its prognostic value is still controversial. Bone metastases from prostate cancer are generally classified as osteoblastic due to increased bone formation. However, this categorization is probably oversimplified since there are overlapping bone cell activities between osteoblastic and osteolytic metastases. Prostate cancer bone metastases can also have a myeloma-like radiological appearance, but little is known about this subgroup of lesions. 

Aims: The aims of this work were as follows: a) to evaluate outcomes after surgery in patients with MSCC as the IMM; b) to analyse the prognostic value of the SINS regarding survival and neurological function after surgery for MSCC in patients with prostate cancer and haematological malignancies; and c) to analyse the clinical and morphological features of prostate cancer spinal bone metastases with a myeloma-like radiological appearance. 

Patients and methods: In studies I-III, we retrospectively evaluated the outcomes after surgery for MSCC in patients with MSCC as the IMM (study I, n=69), prostate cancer (study II, n=110) and haematological malignancies (study III, n=48). In study IV, tumour tissue samples from bone metastases obtained during surgery for MSCC in 110 patients with prostate cancer were analysed by immunohistochemistry and molecular transcriptomic analyses, and the results were related to the radiological appearance and clinical outcomes. 

Results: Study I: The primary tumour was identified in 59 of 69 patients. The median postoperative survival after surgery for MSCC was 20 months. Patients with prostate cancer had the longest median survival (6 years), and patients who were defined as having cancer of unknown primary tumour had the shortest median survival (3.5 months). Surgery maintained and improved the ability to walk in these patients. Study II: A total of 106 of 110 patients met the SINS criteria for potential instability or instability. There was no statistically significant difference in the overall risk of death between the SINS potentially unstable and unstable SINS categories, or in the risk of loss of ambulation one month after surgery. Study III: The median postoperative survival was 71.5 months in patients with myeloma and 58.7 months in patients with lymphoma. The SINS was not related to postoperative survival or neurological outcomes. The ability to walk before surgery was strongly associated with the postoperative ambulatory status. On multivariate Cox regression analysis, the ability to walk and a higher blood haemoglobin level prior to surgery were associated with superior survival. Study IV: A myeloma-like radiological appearance of prostate cancer spinal bone metastases was associated with poor survival and neurological outcomes after surgery for MSCC. 

Conclusions: Patients with MSCC as the IMM resemble a heterogeneous group in which survival is highly dependent on the type of primary tumour. A diagnostic workup is essential before a prognosis can be estimated in order to select candidates for surgery. The SINS may be helpful in selecting patients for surgery for MSCC, but it cannot be used to predict postoperative survival or neurological outcomes in patients with prostate cancer or in patients with haematological malignancies. A myeloma-like radiological appearance of prostate cancer spinal bone metastases is a strong negative predictor for survival and neurological outcomes after surgery for MSCC.