Statistics of Primary Malignant Spine Tumors in Japan: A Retrospective Study Using the Bone and Soft Tissue Tumor Registry in Japan.

Study Design: A retrospective registry-based study.

Objective: To elucidate the nationwide epidemiology, treatment patterns, and prognosis of primary malignant spine tumors (PMST) using the Japanese Orthopaedic Association's Bone and Soft Tissue Tumor (BSTT) Registry.

Summary Of Background Data: PMSTs are rare, comprising a small proportion of primary malignant bone tumors. The surrounding anatomical structures make complete resection challenging, leading to poor prognoses. Studies using the Surveillance, Epidemiology, and End Results database have provided valuable epidemiological insights; however, limitations in the granularity and diversity of histological subtypes persist, leaving detailed knowledge of PMSTs insufficiently clarified.

Methods: We analyzed 288 PMST cases from the BSTT Registry (2006-2019), evaluating patient demographics, tumor characteristics, treatment details, and prognostic outcomes. Kaplan-Meier methods estimated disease-specific survival (DSS), and Cox proportional hazards models identified prognostic factors.

Results: PMSTs accounted for 3.3% of primary malignant bone tumors. Common histological subtypes included osteosarcoma (21.9%), chondrosarcoma (16.3%), chordoma (13.9%), and undifferentiated pleomorphic sarcoma (13.9%). Surgery was performed in 46.2% of cases, with intralesional margins in 54.1%. Chemotherapy and radiotherapy were administered in 42.0% and 54.9% of cases, respectively. The 5-year DSS was 47.5%. Adjusted analysis revealed favorable prognoses for chondrosarcoma (hazard ratio [HR]: 0.23, 95% confidence interval [CI]: 0.06-0.87, P=0.031), chordoma (HR: 0.27, 95% CI: 0.09-0.84, P=0.024), and Ewing sarcoma (HR: 0.42, 95% CI: 0.18-0.98, P=0.044) compared to osteosarcoma. Adults (40-64 years) had better outcomes than the elderly (≥65 years; HR: 0.43, 95% CI: 0.24-0.76, P=0.015). Advanced TNM stage (IVA + IVB) was an adverse prognostic factor (HR: 7.60, 95% CI: 1.85-31.18, P=0.005).

Conclusions: PMSTs are rare and present diverse histological subtypes with poor prognoses. This study emphasizes the need for further investigations to optimize PMST management and improve prognoses.

Level Of Evidence: 2b.