From basic immunobiology to the upcoming WHO-classification of tumors of the thymus. The Second Conference on Biological and Clinical Aspects of Thymic Epithelial Tumors and related recent developments.

The Second Conference on Biological and Clinical Aspects of Thymic Epithelial Tumors in Leiden, The Netherlands, 1998, set the stage for an interdisciplinary meeting of immunologists, pathologists and members of various clinical disciplines to exchange their recent findings in the field of thymus-related biology, pathology, and medicine. The contributions covered such diverse subjects as the role of transcription factors and cytokines in the development of the thymic microenvironment, thymic T, B and NK cell development, the pathogenesis of myasthenia gravis and other thymoma-associated autoimmunities, the pathology of thymic epithelial tumors and germ cell neoplasms, and new approaches to their diagnosis and treatment. This editorial will briefly sum up the data presented at the Conference and will comment on related novel findings that have been reported since then. Because it was also at the Leiden Conference, that the proposal of the WHO committee for the classification of thymic tumors was discussed for the first time, a description of the upcoming WHO Classification of Tumors of the Thymus is given with emphasis on the diagnostic criteria of thymic epithelial tumors, that should now be termed as type A, AB, B1-3 and type C thymomas, to make pathological and clinical studies comparable in the future.