The 5th Edition of the World Health Organization Classification of Hematolymphoid Tumors

  The WHO classification of tumors of various organ systems, also known as the WHO Blue Books, has provided a unified tumor classification system enabling people across the world to share their knowledge and research results. Newer editions with updates have been made every five to ten years to reflect our better understanding of these diseases through the ongoing research work conducted by many researchers and physicians. The last edition of the WHO classification of hematolymphoid tumors was the 4th edition released in 2008 and revised in 2017. Recently, the 5th edition of the WHO classification of hematolymphoid tumors was released, with the online version available since August 2022, and the print version expected to be out at the end of 2022. The 5th edition has been completely rewritten with numerous changes and updates, which include revised hierarchical classification structure, addition or deletion of entities or subtypes, changes or revisions of terminology or nomenclature, revisions or changes of diagnostic criteria, and updates of pathogenesis, clinical and genetic features. Stroma-derived tumors of lymphoid tissue and tumor-like lesions have been included for the first time. This chapter provides a brief overview of the 5th edition of the WHO classification of hematolymphoid tumors with a focus on the changes and updates from a reader’s perspective.