Diagnostic Challenges in WHO Classification of Thymic Epithelial Tumors: The Clinical Value of an International Expert Pathology Panel

This is the authors' abstract. We don't add key points for this paper.

Background Thymic epithelial tumors (TETs) are rare mediastinal tumors classified according to the WHO classification system. Classification can be challenging due to overlapping histological features. Subtyping on biopsy specimens is often inaccurate due to tumor heterogeneity and sampling effect. Since 2012 an international thymic tumor pathology expert panel is available in the Netherlands. This study evaluates the added value of this panel by assessing the discrepancies in diagnosis, inter-observer agreement and concordance on diagnosis between biopsy and the subsequent resection specimen. Methods All pathology excerpts from 2012 until 2024 for patients diagnosed with a thymic tumor were extracted from the national PALGA database and evaluated for histological subtype, assessment and the thymoma panel result. Results In total 1163 resection and 304 biopsy specimens were included, of which 36.1% were submitted to the thymoma panel. The diagnosis changed in 15.7% of cases after assessment. The subtypes AB and Bmix were most often submitted to the thymoma panel and the diagnosis changed most often for subtype A, B3 or Bmix. In 72.8% the concordance between the panel members exceeded 90%. The biopsy diagnosis varied from the resection diagnosis in 46.8%, but the differentiation between thymoma and thymic carcinoma was accurate on biopsy. Conclusion A panel of dedicated pathologists with experience in thymic abnormalities contributed substantially to a more accurate classification of TETs, thereby guiding optimal treatment planning and prognostic evaluation. Despite the discrepancies between biopsy and resection specimens, distinguishing thymoma from thymic carcinoma was accurate on biopsy.