The Ninth Edition TNM Staging System for Thymic Epithelial Tumors: A Comprehensive Review

Accurate cancer staging is essential for guiding treatment decisions and predicting outcomes. The TNM classification is based on three principal elements: size and extent of the primary tumor (T), the degree of spread to regional lymph nodes (N), and the presence of distant metastases (M). In thymic epithelial tumors, clinical TNM staging relies predominantly on cross-sectional imaging, particularly CT and MRI, placing radiologists at the forefront of staging accuracy. Their assessments substantially impact both clinical decision-making and the quality of data in staging registries. A major update in this field is the ninth edition of the TNM classification for thymic epithelial tumors, effective January 2025, which refines TNM category definitions to improve staging accuracy and clinical applicability. This review article outlines these updates, illustrating their application through case examples, and emphasizes the radiologist's crucial role in cancer staging, including selection of appropriate imaging techniques, interpretation of key radiologic features, and effective communication of findings to multidisciplinary teams. These insights aim to enhance staging precision and improve patient outcomes in thymic malignancies. Keywords: Thymus, Staging © RSNA, 2025.