The IASLC Thymic Epithelial Tumors Staging Project: Proposals for the N and the M Components for the Forthcoming (9th) Edition of the TNM Classification of Malignant Tumors.

INTRODUCTION: Stage classification is an important underpinning of management in patients with cancer, and rests on a combination of three components: T for tumor extent, N for nodal involvement, and M for distant metastases. This article details the revision of the N and the M components of thymic epithelial tumors for the 9th edition of the TNM classification of malignant tumors proposed by the Thymic Domain of the International Association for the Study of Lung Cancer Staging and Prognostic Factors Committee.

METHODS: The N and M components of the 8th edition staging system were verified by a large international collaborative data source through a data-driven analysis. A total of 9,147 cases were included for analysis, including 7,662 thymomas, 1,345 thymic carcinomas, and 140 neuroendocrine thymic tumors.

RESULTS: Lymph node involvement rates were 1.5% in thymomas, 17.6% and 27.7%, respectively in thymic carcinomas and neuroendocrine thymic tumors. Rates of lymph node metastasis were increasingly higher in tumors with higher T stage and higher grade histology. Survival analysis validated the differences in the N and M categories proposed in the 8th edition staging system. Good discrimination in overall survivals was detected among pathologic (p)N and pM categories in patients with thymoma and thymic carcinoma.

CONCLUSIONS: No changes are proposed from the 8th edition for the N and M components. The proposed stage classification will provide a useful tool for management of the disease among the global thymic community.