New TNM Staging System for Thymic Malignancies

In patients with malignant tumors, the TNM classification has been widely used by clinicians as a guide for estimating prognosis, and is the basis for treatment decisions. Recently, the International Association for the Study of Lung Cancer Staging and Prognostic Factors Committee and the International Thymic Malignancy Interest Group have proposed a new classification for thymic malignancies to be included in the next official staging system of the forthcoming 8th edition of the TNM classification. In this study, we reviewed 154 consecutive patients with thymic epithelial tumors who underwent complete resection at our institution, and compared their characteristics and outcomes when classified according to the proposed system with those when classified under the current Masaoka-Koga system. The proportion of patients with stage I disease increased markedly to 77.3% under the proposed system because a certain number of patients with Masaoka-Koga stages II and III diseases were downstaged to the new stage I. Regarding histology, among 69 patients with type A, AB, or B1 thymoma, 68 tumors (99%) were diagnosed as new stage I disease. When using the proposed system, the recurrence-free survival rates showed significant deterioration with increasing stage, while the overall survival rates did not. Although the new TNM classification does not serve as an effective prognostic prediction model for overall survival, it appears to offer some benefit, especially in the analysis of recurrence-free survival.