Survival and prognostic factors in patients with stable and unstable spinal bone metastases from solid tumors: a retrospective analysis of 915 cases

Background: Adequate prediction of survival plays an important role in treatment decisions for patients with spinal bone metastases (SBM). Several prognostic factors are already used in daily clinical practice, but factors related to stability of SBM are still unknown. Therefore, we designed this study to identify these prognostic factors. Methods: We retrospectively assessed 915 patients from solid tumors with commonly metastased into the bone treated at our department between January 2000 and January 2012. Lung cancer (NSCLC), breast and renal cancer listed in Table 1 are the most common solid tumors with bone metastasis in this study. Prostate carcinoma was excluded due to osteoblastic SBM with no influence for stability. We calculated overall survival (OS) and bone survival (BS; time between first diagnosis of bone metastases until death) with the Kaplan-Meier method and assessed prognostic factors for BS with the log-rank test and a Cox regression model separately for patients with stable and unstable SBM. Results: Median follow-up was 9.3 months. OS after 6 months, 1, 2, and 5 years was 81, 62, 42, and 25 % in patients with stable SBM and 78, 57, 38, and 22 % in patients with unstable SBM (p = 0.851). BS was 57, 38, 22, and 5 % in the group of stable SBM after 6 months, 1, 2, and 5 years. For patients with unstable SBM BS after 6 months, 1, 2, and 5 years was 59, 39, 19, and 8 % (p = 0.755). In multivariate analysis we found male gender (HR = 1.27 [95 % CI 1.01-1.60], p = 0.04), Karnofsky performance status (KPS) < 80 % (HR = 1.27 [95% CI 1.04-1.55], p = 0.02) and non-small cell lung cancer (NSCLC; HR = 2.77 [95% CI 1.99-3.86], p < 0.0001) to be independent prognostic factors for shortened survival in patients with stable SBM. Independent prognostic factors for unstable SBM were age per year (HR = 1.01 [95 % CI 1.0-1.02], p = 0.025), multiple SBM (HR = 1.35 [95 % CI 1.1-1.65], p = 0.003), and NSCLC (HR = 2.0 [95 % CI 1.43-2.80], p < 0.0001). Additionally, not wearing an orthopedic corset (HR = 0.77 [95 % CI 0.62-0.96], p = 0.02) was associated with prolonged BS in patients with unstable SBM and in both groups BS was significantly longer in patients without liver metastases (stable SBM: HR = 0.72 [95 % CI 0.56-0.92], p = 0.008; unstable SBM: HR = 0.71 [95 % CI 0.54-0.92], p = 0.01). Conclusions: Survival was equal for patients with stable and unstable SBM. However, prognostic factors differed in both groups and stability should therefore be considered in treatment decision-making.