Long-term Outcomes for Extraskeletal Myxoid Chondrosarcoma: A SEER Database Analysis

Background: Extraskeletal myxoid chondrosarcoma (EMCS) is a rare tumor that typically has an indolent course but high rate of recurrence. We queried the Surveillance, Epidemiology, and End Results (SEER) database to assess factors associated with metastasis, treatment, and survival. Methods: We queried the SEER 1973-2016 database for patients with myxoid chondrosarcoma (ICD-O-3: 9231/3). Kaplan-Meier analyses and Cox proportional hazard models assessed effects on overall survival (OS) of demographics and clinical characteristics. Logistic regression assessed associations between tumor location and distant disease. Primary analysis was a complete case analysis; multiple imputation (MI) was used in a sensitivity analysis. Results: Locoregional disease (LRD) was found in 373 (85%) of patients. In univariate analysis with LRD, surgery correlated with superior OS [HR = 0.27; 95% confidence interval (CI), 0.16-0.47]; chemotherapy and radiotherapy associated with inferior OS (HR = 1.90; 95% CI, 1.11-3.27 and HR = 1.45; 95% CI, 1.03-2.06, respectively). No treatment modality associated with OS in the adjusted, complete case model. In the adjusted sensitivity analysis, surgery associated with superior outcomes (HR = 0.36; 95% CI, 0.19-0.69). There was no OS difference by primary tumor site. 10-year OS with distant disease was 10% (95% CI, 2%-25%). Conclusions: Surgery in LRD associated with improved OS in univariate analysis and adjusted models correcting for missing data. There was no OS benefit with chemotherapy or radiotherapy. Impact: This represents the largest report of EMCS with long-term follow-up. Despite the reputedly indolent nature of EMCS, outcomes with metastatic disease are poor. We provide OS benchmarks and guidance for stratification in future prospective trials.