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

Gender, primary site, age and KPS are well known prognostic factors in tumor disease. However, prognostic factors for survival related to initial stability of SBM are still unknown. Therefore, the objective of this retrospective study with 915 patients was to assess prognostic factors for survival related to stability of SBM. Adequate prediction of survival is important in deciding on treatment for patients with SBM. In our study we found no difference in BS or OS between patients with stable and unstable SBM. This is in agreement with previous reports in which stability did not influence survival. Neither in lung cancer, with an extremely short survival time [8], nor in breast cancer, with a significantly better prognosis [12], did stability of SBM effect survival times. However, we were able to show that prognostic factors for bone survival differ between patients with stable and unstable metastases. For stable SBM gender, KPS, and primary site were identified as prognostic factors. Number of metastases, age, primary site, and wearing of an orthopedic corset were prognostic factors in patients with unstable SBM. In both groups visceral metastases, particularly liver metastases, were associated with a significantly shorter survival. Previous studies on prognostic factors for survival after diagnosis of bone metastases support our result. A recent study identified five factors in elderly breast cancer patients as independent predictors of survival: visceral metastases, time developing motor deficits, ambulatory status, performance score, and number of involved vertebrae [2, 13]. In another previous study symptomatic spinal metastases, pretreatment albumin level, primary cancer site, KPS, and number of visceral metastases were associated with survival [3]. 46 % of the patients in our study suffered from lung cancer (NSCLC), most of which were males, with a poor prognosis whether the bone lesions are stable or unstable [8]. On the other hand women with breast cancer, 20 % in our study, have a better prognosis in BS and OS [12]. Patients with multiple bone metastases [14] are frequently those requiring an orthopedic corset. The additionally immobilization may worsen morbidity and quality of life in those patients, which in turn could explain the significantly reduced survival probability. In a recent study we demonstrated that the incidence of pathological fractures is not significantly increased without a surgical corset [15]. We thus believe that clinicians should focus more on patients’ individual situations when prescribing surgical corsets. Concomitant bisphosphonate treatment did not influence survival in our analysis. We believe that the median follow-up of 9.3 months might have been too short to detect any effects of bisphosphonate therapy. In a study in 2004 bisphosphonate therapy itself contains a 9-months core phase and a 12-months extension phase. The final analysis in this study was performed at 21 months after therapy. Here median time to first skeletal-related events was prolonged by nearly 4 months, so we conclude the benefit for stability can only be demonstrated in a longer follow-up [16].

This study is focusing on stability and survival time, thus other factors such as pain, quality of life, neurologic indication, data on additional osteolytic or osteoblastic lesions, operative stabilization, co-morbidity, pathologic fractures or incidence of new metastases are not recorded in this analysis. This should be included in further investigations. Data on time between first diagnosis of cancer and first diagnosis of bone metastases were not available in the dataset. Therefore, this analysis cannot differentiate between patients with early or late onset metastases. However, in ovarian cancer diagnosis of late-onset bone metastases hardly influenced the prognosis at all [17].

This study underlined that limited disease, male gender, age, performance status and certain primary sites such as NSCLC are prognostic factors for survival. Importantly, prognostic factors differed between patients with stable und unstable SBM. Therefore, stability should be considered in treatment decision-making, despite that BS and OS did not differ between patients with stable and unstable SBM.