The New WHO Nomenclature: Lymphoid Neoplasms

Extract

The World Health Organization (WHO) project of classifying tumors of the hematopoietic and lymphoid tissues began in 1995 as a collaborative effort of the European Association for Haematopathology and the Society for Haematopathology. The WHO classification is based on the premise that a classification should define distinct diseases by using all available information instead of relying on one or two major criteria.¹ To that end they used as a starting point the principles defined in the Revised European American Classification of Lymphoid Neoplasms (REAL), published in 1994 by the International Lymphoma Study Group.² The REAL classification uses morphology, immunophenotype, genetic features, and clinical features to define an entity. The relative importance of each of these features varies among diseases, i.e., there is no one ‘gold standard’. Morphology is always important, but other adjuncts are more characteristic than others in specific subtypes, e.g., immunology might be an important criterion in one disorder, while cytogenetics may be the defining characteristic in another. Although considerable controversy was provoked by the publication of the REAL classification, experience over the next six years proved that the system was reproducible when used by expert hematopathologists.³

The WHO classification proposes stratifying lymphoid neoplasms into B cell, T/NK cell neoplasms, and Hodgkin's lymphoma (Hodgkin's disease). The next level of classification separates T and B cell neoplasms into precursor (lymphoblastic) versus mature cell conditions. These are then further subdivided into clinical presentations: leukemic, primary extranodal, and nodal diseases. As to be expected with the lymphoid neoplasms, there is still…

ABBREVIATIONS: ALL = acute lymphoblastic leukemia; AML = acute myelogenous leukemia; FAB = French-American-British; FLC = follicular large cell lymphoma; FMC = follicular mixed cell lymphomas; FSC = follicular small cleaved lymphomas; LBL = lymphoblastic lymphoma; REAL = Revised European American Classification of Lymphoid Neoplasms; WHO = World Health Organization.