The IASLC Thymic Epithelial Tumors Staging Project: Proposal for a Stage Classification for the Forthcoming (9 th ) Edition of the TNM Classification of Malignant Tumors.

INTRODUCTION: A tumor, node, metastasis (TNM)-based system for all types of thymic epithelial tumors (TET) was introduced in the 8th edition of the TNM classification of thoracic malignancies. The Thymic Domain of the Staging and Prognostic Factors Committee of the International Association for the Study of Lung Cancer, composed of multispecialty international experts, was charged to develop proposals for the 9th edition. This article outlines the proposed definitions for the T, the N and the M components, and their combination into stage groups.

METHODS: A large central database of 11,347 patients with TET was assembled thanks to the contribution of the major thymic organizations worldwide and analyses were carried out for the T, the N, and the M components and the stage groups. Overall survival was the outcome measure for patients with completely and incompletely resected tumors, and recurrence, for those with complete resection. When the number of patients was sufficient, analyses were performed separately for thymomas, thymic carcinomas and neuroendocrine thymic tumors.

RESULTS: Tumor size is included in the T1 category as T1a (≤ 5cm) and T1b (>5 cm); the mediastinal pleura is dropped as a T descriptor; invasion of the lung or phrenic nerve is reclassified as T2 (instead of T3). No changes are proposed for the N and the M components from the 8th edition. The stage groups remain the same.

CONCLUSIONS: The proposed changes for the 9th edition of the TNM classification sets the stage for further progress in the future for these rare tumors.