The International Association for the Study of Lung Cancer Thymic Epithelial Tumors Staging Project: Proposals for the N and the M Components for the Forthcoming (Ninth) Edition of the TNM Classification of Malignant Tumors

Making an accurate diagnosis of anterior mediastinal lesions: a proposal for a new diagnostic algorithm from the BTOG Thymic Malignancies Special Interest Group

Due to the rising demand in cross-sectional thoracic imaging, anterior mediastinal lesions are being identified with increasing frequency. Following iterative and multidisciplinary discussions, the BTOG Thymic Malignancies Special Interest Group have developed an algorithm to standardise the diagnostic approach for these relatively uncommon but important conditions which span from benign (thymic remnant, thymic hyperplasia and thymic cysts) to suspected localised thymomas to suspected more aggressive malignancy (thymic carcinoma, lymphoma and germ cell tumours). For each condition, we provide a brief description, an overview of the key radiological findings and a description of the proposed algorithm including the rationale behind the recommendations. We also highlight the role of magnetic resonance (MR) imaging for the characterisation of anterior mediastinal masses in specific indications when the necessary local resources and expertise exist. In addition, we hope this provides the rationale for service development in MR of the anterior mediastinum where current resource and expertise requires development. Through this standardised pathway, we hope to drive improvements in patient care by rationalising surveillance schedules, avoiding unnecessary resections of benign entities with their associated morbidity and optimising the diagnostic work-up prior to the appropriate treatment of anterior mediastinal malignancies.

TNM Staging System in Thymoma: A Critical Appraisal?

Thymomas are rare tumors of the anterior mediastinum with peculiar clinical and pathological features. They have been deeply analyzed by pioneer authors, who strictly linked their name to the main pathological and staging classifications. Before the latest edition of the WHO classification of thymic epithelial tumors, the history of thymoma pathological classification inherited the name of the pathologists who systematically addressed the issue, from Levine-Rosai to Muller-Hermelink. Similarly, the thymoma staging system is intimately related to the name of two surgeons, Masaoka and Koga, who historically dealt with this disease. More recently, the traditional tumor-nodes-metastasis (TNM) system has been developed for the staging of this condition, in a rational attempt to put thymomas in conformity with the other solid tumors. The efforts of the International Thymic Malignancies Interest Group (ITMIG) and the Thymic Domain of the Staging and Prognostic Factors Committee (TD-SPFC) of the International Association for the Study of Lung Cancer (IASLC) resulted in the TNM classification of thymic tumors, which have been included in the eighth edition of the American Joint Committee on Cancer's (AJCC) Cancer Staging Manual. Herein, we report a narrative review of the evolution of the thymic epithelial tumors (TET) staging system and present a critical appraisal of the actual TNM classification compared with the historical Masaoka-Koga classification, with special focus on the proposal for the ninth edition of the TNM, expected in 2024.

The International Association for the Study of Lung Cancer Thymic Epithelial Tumor Staging Project: A Re-Assessment of the International Thymic Malignancy Interest Group/International Association for the Study of Lung Cancer Lymph Node Map for Thymic Epithelial Tumors for the Forthcoming Ninth Edition of the TNM Classification of Malignant Tumors

INTRODUCTION

A lymph node map is the pillar on which accurate assignment and documentation of nodal classification stands. The International Thymic Malignancy Interest Group created the first map for thymic epithelial malignancies in conjunction with the eighth edition of the TNM classification, representing the first official TNM classification of thymic epithelial malignancies. The map was based on clinical experience and published studies, but it was largely empirical because of limited available data. Dissemination of the map and implementation of a standard thymic stage classification across the world in 2017 have provided more consistent and granular data.

METHODS

More than twice as many cases of node involvement are available for analysis in the current database compared with that of the eighth edition database, allowing validation of many aspects of the eighth edition map. This article details the process and considerations for refinement of the thymic map for the ninth TNM used by the Thymic Domain of the Staging and Prognostic Factors Committee of the International Association for the Study of Lung Cancer. The committee evaluated a large international collaborative data set, published anatomical and clinical studies pertaining to lymph node spread from thymic epithelial tumors, in conjunction with the analysis underlying refinements of the TNM components for the ninth edition TNM classification.

RESULTS

The node map boundaries of the N1 and N2 categories remain unchanged. Visual clarifications have been added to the nomenclature of nodal stations within these regions.

CONCLUSIONS

On the basis of the recommendation to keep the N component unchanged for the ninth edition TNM classification, the lymph node map remains unchanged as well; however, clarifications have been added to facilitate clinical use.