Page 55 - Predicting survival in patients with spinal bone metastasesL
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                                Performance status was dichotomized into normal functioning (KPS 100-80%) and impaired functioning (KPS 70-10%). Neurological functioning was inferred from clinical exams and divided into three groups: no deficit present (Frankel E), minor motor or sensory deficit (Frankel D) and major motor or sensory deficit (Frankel A, B, C). The number of spinal and extraspinal bone metastases was obtained from radiology reports and further subdivided in three categories according to Tokuhashi9.
Statistical analysis
Survival time was calculated as the difference between start of treatment for the spinal metastasis and date of death or the last follow-up moment recorded. Survival curves were estimated using the Kaplan-Meier method. Follow-up was assessed by employing the reverse Kaplan-Meier method18. Cox proportional hazard models were fitted using Collett’s method, consisting of a univariate analysis, followed by multivariate backward and multivariate forward selection19. Harrell’s c-statistic was used for external validation of the predictive accuracy of the presented model20. It estimates the probability of concordance between predicted and observed responses. Survival curves were compared using log-rank tests. A p-value of <0.05 was considered statistically significant. All analyses were performed using SPSS 20.0, SPSS Inc., Chicago IL.
RESULTS
A total of 1301 patients were treated for symptomatic spinal metastases during the study period. After excluding patients with direct ingrowth of a primary tumor into the vertebra (n=23), patients with bone metastases in the sacral or sacroiliac region (n=105), leptomeningeal metastases (n=24), intradural metastases (n=14), metastases deriving from primary tumors of hematological or of unknown origin (n=44) and metastases deriving from rare primary tumors (n=42), 1049 patients remained eligible for analysis. Primary tumors classified as adenocarcinoma of unknown primary (ACUP) were not excluded. Six patients moved abroad shortly after finishing treatment and were lost to follow-up (figure 1).
IV
PREDICTIVE MODEL
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