Evidence-based Tumor Staging of Skeletal Chondrosarcoma

Supplemental Digital Content is available in the text. The eighth edition of the American Joint Committee on Cancer (AJCC) staging system has introduced major changes for the staging of skeletal sarcomas. However, it is unclear if these changes improve the predictive value for chondrosarcomas of the nonpelvic appendicular and nonspinal axial skeleton. Specifically, there is no clear evidence that supports the use of the proposed binary size cutoff of 8 cm for risk stratification, nor is a rationale provided for the categorization of grade 2 chondrosarcomas as high grade. The prognostic value of various anatomic and pathologic factors including tumor size, histologic grade, site of metastasis, and local tumor extent was evaluated using a cohort of patients derived from the National Cancer Database (N=3946). A simplified evidence-based staging system for chondrosarcoma (the Vanderbilt Staging System) was developed based on histologic subtype, histologic grade, and presence of metastatic disease. The predictive accuracy for 5-year overall survival was evaluated for the AJCC 8th edition, Musculoskeletal Tumor Society, and Vanderbilt Staging Systems by comparing areas under receiver operating characteristic curves generated from logistic regression analysis. Three different concordance indices and Bayesian information criterion were also calculated for model comparisons. The Vanderbilt Staging System showed significantly improved predictive accuracy for 5-year survival (82±2%) compared with the AJCC (79±2%; P=0.0075) and Musculoskeletal Tumor Society systems (76±2%; P<0.00005) in a separate validation cohort. Furthermore, the Vanderbilt Staging System showed significantly higher concordance with clinical outcomes for 2 of 3 examined indices and significantly greater extent of explained variation compared with the other 2 staging systems.