Overview of 2008 WHO Classification of Malignant Lymphoma

Lymphoma classification is now evolving. The 4th edition of the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues was published in 2008, regarded as a revised and updated version of the 2001 3rd edition; an effort that involved 138 authors from 22 countries and two clinical advisory committees comprising 62 clinical specialists with expertise in lymphoid and myeloid disorders. New aspects of the 2008 WHO classification can be briefly summarized as follows: 1) a greater recognition of "early" lesions, i.e., an incipient neoplasm, e.g., in situ follicular lymphoma, has been incorporated; 2) age was highlighted as a defining feature of some neoplasms, e.g., EBV+ diffuse large B-cell lymphoma of the elderly, pediatric follicular lymphoma, and EBV+ T-cell lymphoproliferative diseases of childhood; 3) anatomical sites were noted as having an important impact on disease definitions; and 4) newly recognized borderline categories were listed on the basis of their biological overlap between diffuse large B-cell lymphoma and Burkitt lymphoma or classical Hodgkin lymphoma.