The 2008 WHO classification of lymphomas: implications for clinical practice and translational research

The 4(th) edition of the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues published in 2008 builds upon the success of the 2001 3(rd) edition; new entities are defined, and solutions for problematic categories are sought. Recent studies have drawn attention to the biological overlap between classical Hodgkin lymphoma (CHL) and diffuse large B-cell lymphomas (DLBCL). Similarly, there is a greater appreciation of the borderlands between Burkitt lymphoma and DLBCL. Strategies for the management of these borderline lesions are proposed. Additionally, age-specific and site-specific factors play an important role in the definition of several new entities, which also have biological underpinnings. Among the peripheral T-cell lymphomas (PTCL), more precise definitions were introduced for several entities, including anaplastic large cell lymphoma, angioimmunoblastic T-cell lymphoma, enteropathy-associated T-cell lymphoma, and subcutaneous panniculitis-like T-cell lymphoma. Several new variants of primary cutaneous T-cell lymphomas are proposed. Finally, the subclassification and categorization of the most common lymphoma subtypes, follicular lymphoma (FL) and DLBCL, were altered to enhance diagnostic accuracy and aid in clinical management. The 2008 WHO classification also draws attention to early events in lymphomagenesis. These lesions help delineate the earliest steps in neoplastic transformation and generally mandate a conservative therapeutic approach. The 2001 classification was rapidly adopted for clinical trials and successfully served as a common language for scientists comparing genetic and functional data. The modifications made in the 2008 classification are the result of this successful partnership among pathologists, clinicians, and biologists, but are only a stepping stone to the future.