Abstract
Background and Purpose
Up to 70% of cancer patients with terminal illness have bone metastases, with the spinal column being most affected. The standard local treatment for painful spinal metastases is conventional external beam radiotherapy. However, ~30–40% of the patients do not achieve adequate pain relief. It is not well understood why some patients respond and others do not. Considering the limited life expectancy of these patients it is crucial to optimize treatment selection to ensure fast, effective and lasting symptom relief. We hypothesized that pain resulting from mechanical instability of the vertebra responds less well to radiotherapy than pain originating from local tumor effects. The aim of this study was to investigate the relationship between spinal instability, defined by the Spinal Instability Neoplastic Score (SINS), and the response to palliative radiotherapy for symptomatic spinal metastases.
Material and Methods
A prospective international multicenter observational study of patients who underwent irradiation of symptomatic spinal metastases was performed between January 2013 and December 2014. Patients were excluded if they were diagnosed with multiple myeloma, if they had previous surgery on the same level or if they had substantial neurological deficits (ASIA ≤C). The SINS was calculated by an observer blinded to outcome using the radiotherapy planning computed tomography scans. Pain response was rated using the International Bone Metastases Consensus Working Party Endpoints. The association between SINS and response was estimated by multivariate logistic regression analysis.
Results
A total of 155 patients were included, 91 male and 64 female (mean age 66 ± 11 years). Thirteen patients (8%) died within four weeks following treatment, 18 (12%) patients were lost to follow-up. Neither median nor mean SINS was significantly different for patients with or without response. In multivariate analysis, the SINS was not significantly associated with response (adjusted odds ratio 0.94; 95% confidence interval 0.81–1.10; p = 0.449). The WHO performance score, however, was related to radiotherapy response.
Conclusion
No significant relationship was observed between degree of mechanical spinal instability, as reflected by the SINS, and response to radiotherapy. Trying to explain our findings, it can be argued that some components of SINS reflect current mechanical instability while other components are indicative of impending instability. Future studies should aim to optimize the definition of instability to better predict treatment outcome.