The WHO (2008) classification of B-cell lymphomas - basics and important changes

Abstract

In 2008, the World Health Organization published a revised and updated edition of the classification of lymphoid tissues tumors. Within the category of indolent B-cell lymphomas there appeared new definitions and diagnostic criteria for established diseases such as chronic lymphocytic leukemia and Waldenstöm’s macroglobulinemia. New provisional entities were introduced such as splenic B-cell lymphoma/leukemia, unclassifiable, splenic diffuse red pulp small B-cell lymphoma and hairy cell leukemia - variant. Clinically different pediatric follicular lymphoma and pediatric nodal marginal zone lymphoma have been singled out. ”Early” lymphoid proliferations with still undetermined clinical significance have been described such as monoclonal B-cell lymphocytosis, follicular and mantle cell lymphoma in situ. Diversity of morphological, biological and clinical features of diffuse large B-cell lymphoma (DLBCL) has served as basis to division into variants, subgroups, subtypes and clinico-pathological entities. Morphological variants, molecular subgroups based on gene-expression profiling (germinal center B-cell like and activated B-cell like) and immunohistochemical subgroups of DLBCL were included into an entity called DLBCL, not otherwise specified. New distinct DLBCL subtypes based on topography were defined to include primary DLBCL of the CNS and primary cutaneous DLBCL, leg type. The importance the role of Ebstein-Barr virus (EBV), human herpesvirus 8 (HHV-8) and immunodeficiency status in DLBCL pathogenesis served as basis for introduction of new clinico-pathological entities such as EBV positive DLBCL of the elderly, DLBCL associated with chronic inflammation and large B-cell lymphoma arising in HHV8-associated multicentric Castleman disease. Two new large B-cell lymphomas with features of DLBCL overlap with Burkitt lymphoma or classical Hodgkin lymphoma have been introduced.