Impact of the TNM staging system for thymoma

Abstract

Background: Masaoka-Koga staging system remains the most frequently applied clinical staging system for thymic malignancy. However, the International Association for the Study of Lung Cancer (IASLC)/International Thymic Malignancy Interest Group (ITMIG) proposed a tumor-node-metastasis (TNM) staging system in 2014. This study aims to evaluate its impact on stage distribution, clinical implementation, and prognosis for thymomas. Methods: We performed a single institution, retrospective analysis of 245 consecutive patients who underwent surgical resection for thymoma. 9 patients with thymic carcinoma were excluded. No patients were lost to follow up. Kaplan-Meier survival analysis was used to calculate overall survival. Results: Median age was 62 years; 129 patients (53%) were female. The median overall survival was 158 months (range, 108-208 months), and disease-free survival 194 months (range, 170-218 months). At the end of follow up 63 patients were dead. Early Masaoka-Koga stages I (n=74) and II (n=129) shifted to the IASLC/ITMIG stage I (n=203). 8 patients were down staged from Masaoka-Koga stage III to IASLC/ITMIG stage II because of pericardial involvement. Advanced stages III (Masaoka-Koga: n=30; IASLC/ITMIG: n=22) and IV (Masaoka-Koga: n=12; IASLC/ITMIG: n=12) remained similar and were associated with more aggressive WHO thymoma histotypes (B2/B3). Masaoka-Koga (P=0.004), IASLC/ITMIG staging (P<0.0001) and complete surgical resection (P<0.0001) were statistically associated with survival. At multivariate analysis only R status was an independent prognostic factor for survival. Conclusions: The proportion of patients with stage I disease increased significantly when IASLC/ITMIG system used, whilst the proportion with stages III and IV were similar in both systems. Completeness of resection, Masaoka-Koga and the IASLC/ITMIG staging system are strong predictors of survival. The TNM staging system is useful in disease management and a strong predictor of overall survival.