The WHO 2021 thymoma classification: a work in progress

Abstract

The updated, recently published 2021 WHO classification of thymic tumors incorporates the most recent advances in the field of thymic pathology, with particular emphasis on primary thymic epithelial neoplasms. This new edition retains the basic format of previous editions for the classification of primary thymic epithelial neoplasms reaffirming the schema originally proposed in the first edition, which utilized a combination of letters and numbers for the designation of these tumors. Only minimal changes have been incorporated in the new edition compared with the previous ones. A new helpful feature is a summary in each chapter of recommendations for "essential"and "desirable"criteria to facilitate the diagnosis. A few issues in this classification, however, still require clarification. In this review, the changes and advances in the classification of thymoma presented in the latest WHO book on Thoracic Tumors will be reviewed along with some of the areas that may still benefit from the additional investigation.