Impact of the Spinal Instability Neoplastic Score on Postoperative Prognosis in Patients with Metastatic Cancer of the Cervical Spine

<b>Background:</b> Although the Spinal Instability Neoplastic Score (SINS) is widely utilized to evaluate spinal instability, its prognostic value for survival in patients with cervical spinal metastases remains unclear. This study investigated the association between the SINS and survival outcomes in patients with metastatic cervical spine cancer. <b>Methods:</b> This retrospective cohort study included 106 patients who underwent surgery for metastatic cervical spine cancer at a single institution between 1995 and 2023. Patients were divided into two groups: high SINS (≥13) and low-to-moderate SINS (0-12). Overall survival (OS) was the primary outcome and was analyzed using Kaplan-Meier estimates and Cox regression. Secondary outcomes included changes in Eastern Cooperative Oncology Group Performance Status (ECOG-PS), operation time, estimated blood loss, and postoperative complications. <b>Results:</b> The median OS was significantly shorter in the high SINS group compared to the low-to-moderate SINS group (5.3 months versus 8.6 months; <i>p</i> = 0.023). A high SINS was independently associated with increased mortality risk (hazard ratio [HR], 1.959; 95% CI, 1.221-3.143; <i>p</i> = 0.005). Lung cancer (HR, 4.004; 95% CI, 1.878-8.535; <i>p</i> < 0.001) and rectal cancer (HR, 3.293; 95% CI, 1.126-9.632; <i>p</i> = 0.029) were predictive of worse survival, whereas postoperative chemotherapy (HR, 0.591; 95% CI, 0.381-0.917; <i>p</i> = 0.019) and radiotherapy (HR, 0.531; 95% CI, 0.340-0.827; <i>p</i> = 0.005) were associated with improved survival. Changes in the ECOG-PS and postoperative complication rates were not significantly different between the groups. <b>Conclusions:</b> A high SINS was associated with significantly shorter survival in patients with metastatic cervical spine cancer, reflecting both mechanical instability and tumor aggressiveness.