Spinal Instability as a Prognostic Factor in Patients With Spinal Metastasis of Castration-resistant Prostate Cancer

To evaluate the Spinal Instability Neoplastic Score (SINS) for prediction of survival in patients with spinal column metastasis of castration-resistant prostate cancer (CRPC).

A retrospective study of spinal instability was performed in patients with CRPC using SINS. Overall survival was evaluated starting from the time of SINS evaluation. The subjects were 42 patients with CRPC among 261 cases diagnosed with metastatic spinal tumors by radiologists, among 42,152 cases that underwent a body computed tomography scan at Kawasaki Medical School Hospital within 32 months from December 2013 to July 2016.

The median age was 78 (range=55-91 years), the median prostate-specific antigen (PSA) level at SINS evaluation was 42.1 (0.1-3,121.6) ng/ml, and 11 patients had visceral metastasis. The median periods from diagnosis of bone metastasis and development of CRPC to SINS evaluation were 17 (0-158) and 20 (0-149) months, respectively. The spine was stable in 32 cases (group S) and potentially unstable or unstable in 10 (24%) (group U). The median observation period was 17.5 (0-83) months and 36 patients died. The median survival period after SINS evaluation was longer in group S than that in group U (20 vs. 10 months, p=0.0221). In multivariate analysis, PSA level, visceral metastasis, and spinal instability were significant prognostic factors. The hazard ratio for patients in group U was 2.60 (95%CI=1.07-5.93, p=0.0345).

Spinal stability evaluated using SINS is a new prognostic factor for survival of patients with spinal metastasis of CRPC.