Validation of the Ninth Edition TNM Classification for Thymic Carcinoma After Complete Resection in a High-Volume...

This study aimed to externally validate the ninth edition TNM staging system for thymic carcinoma (TC) in an independent Chinese cohort.

We retrospectively analyzed 245 patients with TC who underwent complete surgical resection between 2010 and 2023. Tumors were staged according to the eighth and ninth TNM editions. Overall survival (OS) and disease-free survival (DFS) were assessed using Kaplan-Meier analysis. Model performance was evaluated using the concordance index (C-index), Akaike Information Criterion, R², and the time-dependent area under the receiver operating characteristic (ROC) curve (AUC).

Compared with the eighth edition, the ninth edition exhibited improved discrimination for OS, with a higher C-index (0.724 versus 0.701), lower Akaike Information Criterion (565.81 versus 568.34), higher R² (0.131 versus 0.121), and superior 5-year AUC (0.693 versus 0.674). Significant differences in OS and DFS were observed between most adjacent stage groups (all p < 0.05), except between stages III and IV. Lung or phrenic nerve invasion was associated with more favorable DFS (5-year DFS: 47.3% versus 27.1%, p = 0.032), supporting reclassification from T3 to T2. Among patients with stage I disease, the Masaoka-Koga staging system provided additional prognostic stratification for DFS, distinguishing between stage I and stage II or higher (5-year DFS: 85.8% versus 56.2%, p = 0.021), whereas no significant difference was observed in OS.

The ninth TNM edition provides improved prognostic discrimination after complete resection, although differentiation between stages III and IV remains limited. The Masaoka-Koga system offers complementary value in early stage disease, particularly for DFS.