Assessing the utility of the spinal instability neoplastic score (SINS) to predict fracture after conventional radiation therapy (RT) for spinal metastases

Purpose Assessing the stability of spinal metastases is critical for making treatment decisions. The spinal instability neoplastic score (SINS) was developed by the Spine Oncology Study Group to categorize tumor-related lesions; however, data describing its utility in predicting fractures in patients with spinal metastases are limited. The purpose of this study is to assess the validity of SINS in predicting new or worsening fracture after radiation therapy (RT) to spine metastases. Methods and materials This is a retrospective analysis of patients treated with conventional RT alone (median total dose, 30 Gy; range, 8-47 Gy; median number of fractions, 10; range, 1-25) for spinal metastasis at Dana-Farber/Brigham and Women's Cancer Center from 2006 to 2013. SINS was calculated for each lesion (range, 0-18). The primary endpoint was time from RT start to radiographically documented new or worsening fracture or last disease assessment. Results A total of 203 patients and 250 lesions were included in analysis. The percentages of lesions with SINS of 0 to 6, 7 to 12, and 13 to 18 were 38.8%, 54.8%, and 6.4%, respectively. Of 250 lesions, 20.4% developed new or worsening fractures; 14.4% for SINS 0 to 6, 21.2% for SINS 7 to 12, and 50.0% for SINS 13 to 18. Multivariate analysis adjusted for sex, age, Eastern Cooperative Oncology Group, histology, and total dose indicated that, compared with stable lesions (SINS 0-6), potentially unstable lesions (SINS 7-12) demonstrated a greater likelihood of new or worsening fracture that was not statistically significant (hazard ratio, 1.66; 95% confidence interval, 0.85-3.22; P = .14), and unstable lesions (SINS 13-18) were significantly more likely to develop to new or worsening fracture (hazard ratio, HR,4.37, 95% confidence interval, 1.80-10.61; P = .001). Conclusions In this study of patients undergoing RT for spinal metastases, 20.4% developed new or worsening vertebral fractures. SINS is demonstrated to be a useful tool to assess fracture risk after RT.