Identification of bone invasion as a poor prognostic factor for spinal synovial sarcoma.

PURPOSE: Synovial sarcoma (SS) is a rare soft-tissue malignancy, with spinal involvement being exceptionally uncommon and associated with poor prognosis. Due to limited data, prognostic factors for spinal SS remain unclear. This study aimed to analyze clinical outcomes and identify prognostic indicators in spinal SS. METHODS: We conducted a retrospective review of 46 SS patients (36 spinal, 10 extremity) treated at our center (2010–2022). Clinical, radiological, and pathological data were analyzed. Treatment strategies included surgical resection (en-bloc where feasible), chemotherapy, and radiotherapy. Bone invasion was assessed via imaging. Prognostic factors for progression-free survival (PFS) and overall survival (OS) were evaluated using Cox regression and Kaplan-Meier analysis. RESULTS: Spinal SS exhibited frequent bone invasion (25/36 cases), a feature rare in extremity SS. The 5-year PFS and OS rates were 33.2% and 35.4%, respectively. Multivariate analysis identified sex(HR 9.81, p = 0.009), bone invasion (HR 20.79, p = 0.003) and Ki-67 ≥ 30% (HR 18.77, p < 0.001) as independent predictors of poor OS. For PFS, prior radiotherapy (HR 4.05, p = 0.017) and Ki-67 ≥ 30% (HR 4.63, p = 0.012) were significant. En-bloc resection improved OS (p = 0.028) but not PFS (p = 0.161). Radiotherapy-naïve patients showed better PFS than pre-irradiated cases. CONCLUSION: Spinal SS demonstrates aggressive behavior, with bone invasion as a potential novel, independent poor prognostic factor. High Ki-67 and prior radiotherapy also predict worse outcomes. En-bloc resection should be prioritized when feasible. These findings highlight the need for tailored management strategies in spinal SS.