Prognostic outcomes of spinal metastasis: timing of metastasis presentation matters

BACKGROUND CONTEXT: Spinal metastasis (SM), though typically associated with late-stage disease, can manifest at any point in the disease process as a synchronous spinal metastasis (SSM) or metachronous spinal metastasis (MSM). The timing of SM presentation can influence the complexity of treatment approaches. Therefore, investigating the clinical and prognostic distinctions between SSM and MSM is vital for enhancing patient management strategies. PURPOSE: This study investigates the incidence, prognosis, and primary malignancies differences between SSM and MSM, aiming to improve clinical practice through inclusion of both surgical and/or radiotherapy cases. STUDY DESIGN/SETTING: A retrospective study at a single tertiary care center in Taiwan. PATIENT SAMPLE: About 4,269 patients aged 18 or older who received surgery and/or radiotherapy for image-confirmed spinal metastasis at a tertiary medical center in Taipei from 2010 to 2022. OUTCOME MEASURES: The primary outcome was the incidence of SSM among patients with SM requiring local treatment. Secondary outcomes included survival differences and primary malignancy distributions between SSM and MSM. METHODS: SSM was defined as SM diagnosed within 31 days of initial cancer diagnosis; MSM was diagnosed later. Missing data was handled with multiple imputation using chained equations. Prognostic differences were analyzed using univariate and multivariate Cox proportional hazards models, and survival outcomes were compared with Kaplan-Meier and log-rank tests. Differences in primary malignancy types and growth rates were evaluated using Chi-square test or Fisher’s exact test. RESULTS: SSM was identified in 19.6% (838/4,269) and MSM in 80.4% (3,431/4,269). SSM patients had a longer median survival than MSM (17.4 months, interquartile ranges [IQR] 5.6–49.0 vs. 7.5 months, IQR 3.0–20.9; p<.001). Lung cancer was the most common primary malignancy, comprising nearly half of SSM cases. Patients with SSM had a more favorable prognosis than MSM (HR=0.74; p<.001). CONCLUSION: One-fifth of the patients were diagnosed with SM before the primary tumor was identified. These SSM patients exhibit distinct clinical and prognostic profiles compared to MSM patients, often showing a survival advantage likely due to their treatment-naïve status and lower tumor burden at time of presentation. These differences suggest that patients with SSM may benefit from tailored treatment approaches, such as more durable surgical stabilization or consideration of higher radiation doses, given their comparatively favorable survival outlook. Future studies should recognize SSM as a unique clinical entity to refine prognostic models and optimize therapeutic approaches.