Head and neck hematolymphoid proliferations: what is new?

In 2024, the World Health Organization published its 5th edition of tumor classification, which comprises several updates and modifications in the "blue book" focused on head and neck tumors. These changes feature a systematized and expanded discussion on haematolymphoid proliferations using a multi-parameter approach that comprises clinical features, morphology, immunophenotype, and genetic data, with the latter becoming an essential characteristic for classification. Moreover, for the first time, the World Health Organization has included non-neoplastic diseases, such as reactive lymphoid proliferations, alongside several recognized independent disorders, including Epstein-Barr Virus positive mucocutaneous ulcers and IgG4-related diseases. Also, various neoplastic diseases, such as paediatric-type follicular lymphoma and large B-cell lymphoma with IRF4 rearrangement, are recognized as independent entities. Finally, the focus has expanded to include different types of histiocytic neoplasms. This review examines and illustrates the main changes and updates on hematolymphoid proliferation and neoplasia in the Head and Neck chapter of the 5th Edition of the Head and Neck WHO classification.