The World Health Organization (WHO) classification of the lymphocytic neoplasms updated in 2016/2017 represents a worldwide consensus on lymphoma diagnosis and is based on two major principles: the stratification of neoplasms according to their cell lineage and their derivation from precursor or mature cells.* The classification recognizes specific diseases based on a combination of morphology; immunophenotype; and genetic, molecular, and clinical features. The WHO classification identifies three main groups of lymphoid malignancies: B-cell neoplasms, T- and natural killer (NK)-cell neoplasms, and Hodgkin lymphoma. In addition to well-defined entities, the classification includes some provisional entities that correspond to categories for which there was insufficient evidence to support its recognition as distinct diseases and borderline categories with overlapping features between large B-cell lymphomas and Burkitt or Hodgkin lymphoma.
Acronyms and Abbreviations
ABC, activated B cell; ALCL, anaplastic large cell lymphoma; ALK, anaplastic lymphoma kinase; ATM, ataxia-telangiectasia mutated gene; BL, Burkitt lymphoma; CLL/SLL, chronic lymphocytic leukemia/small lymphocytic lymphoma; COO, cell of origin; DH, double hit; DLBCL, diffuse large B-cell lymphoma; EBV, Epstein-Barr virus; FISH, fluorescence in situ hybridization; GCB, germinal center B cell; IGH, immunoglobulin heavy chain; IGHV, immunoglobulin heavy chain variable region; ILSG, International Lymphoma Study Group; LBCL, large B-cell lymphoma; LP, lymphocyte predominant; LPL, lymphoplasmacytic lymphoma; MALT, mucosa-associated lymphoid tissue; MCL; mantle cell lymphoma; MZL, marginal zone lymphoma; NF-κB, nuclear factor-κB; NK, natural killer; NOS, not otherwise specified; PMBL: primary mediastinal large B-cell lymphoma; PTCL, peripheral T-cell lymphoma; REAL, revised european-american lymphoma; TdT, terminal deoxynucleotidyl transferase; TH, triple hit; TP53, tumor protein p53 gene; WHO, World Health Organization.
GENERAL ASPECTS OF LYMPHOMA CLASSIFICATION
Lymphocytic neoplasms are a heterogeneous group of diseases with different clinical and biological features. The identification of the specific entities and their particular characteristics are essential to tailor the appropriate management of patients. The World Health Organization (WHO) classification of the lymphoid neoplasms, updated in 2016/2017, represents a worldwide consensus to define the different entities and the criteria for their diagnosis.1 The current principles for the categorization of these neoplasms were established in the Revised European-American Lymphoma classification published by the International Lymphoma Study Group in 1994.2 The international validation of this proposal in a large series of lymphomas from different geographical areas and the integration of the principles of this classification in the third edition of the WHO classification, ended the controversy among pathologists and clinicians in different parts of the world, using different classification schemes with different terminologies and concepts. The major principles to stratify these neoplasms are their cell lineage and their derivation from cells at different stages of differentiation. Some entities, however, do not have a clear normal cell counterpart. The WHO classification identifies four main groups of ...