Lymphoma & related disorders
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WHO classification-B cell


Topic Completed: 5 August 2020

Minor changes: 24 September 2020

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PubMed Search: WHO classification of B cell lymphoid neoplasms 2016

Samantha C. Wu, B.A.
Patricia Tsang, M.D., M.B.A.
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Cite this page: Wu SC, Tsang P. WHO classification-B cell. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/lymphomabcellwho.html. Accessed October 28th, 2020.
Definition / general
  • B cell lymphoma is the most prevalent type of lymphoma and includes the largest number of distinct diagnostic entities among lymphomas
  • 2016 revised World Health Organization (WHO) classification of lymphoid neoplasms incorporates new clinical and genetic data gleaned from modern technologies, e.g. next generation sequencing and FISH, since the previous classification system in 2008 (Expert Rev Hematol 2017;10:405)
  • Includes introduction of new lymphoma entities and updated nomenclature for certain entities to better reflect the clinical features
Highlights of 2016 updated WHO classification
  • More refined subtyping of lymphoma entities based on international consensus enables more targeted therapeutic strategies (Curr Treat Options Oncol 2017;18:45)
  • Current WHO B cell lymphoma classification features the following major updates (Int J Lab Hematol 2017;39:14):
    • Significantly more detailed sorting of B lymphoblastic leukemia / lymphoma based on association with various recurrent genetic abnormalities
    • Lower limit of chronic lymphocytic leukemia cells in blood has been set at 5 × 10⁹/L, below which it may represent either peripheralized small lymphocytic lymphoma or the newly described monoclonal B cell lymphocytosis
    • Newly defined high grade B cell lymphomas, such as the so called double hit or triple hit lymphoma that includes MYC gene rearrangement detectable by FISH
      • Replaces the 2008 diagnostic entity of B cell lymphoma, unclassifiable, with features intermediate between DLBCL and Burkitt lymphoma
    • More refined subtyping of diffuse large B cell lymphomas (DLBCL)
      • Requires determination of DLBCL cell of origin (germinal center B cell type versus activated B cell type); immunohistochemical algorithm acceptable
      • New large B cell lymphoma entities, e.g. fibrin associated diffuse large B cell lymphoma and large B cell lymphoma with IRF4 rearrangement (provisional entity)
    • Renaming of in situ lesions from lymphoma to neoplasia to reflect the low clinical risk observed
      • From in situ follicular lymphoma to in situ follicular neoplasia
      • From in situ mantle cell lymphoma to in situ mantle cell neoplasia
    • Newly designated pediatric lymphoma entity or subtype, e.g. pediatric type follicular lymphoma and pediatric nodal marginal zone lymphoma (provisional subtype)
    • More detailed subtyping of plasma cell neoplasms, including those associated with paraneoplastic syndromes and 3 new myeloma variants
  • B cell neoplasms listed below are based on the WHO's 2016 updated classification of hematopoietic neoplasms (Blood 2016;127:2375)
    • New entities are in italics and provisional entities are marked with an asterisk
Classification of B cell neoplasms (WHO 2016)
Precursor B cell neoplasms:
Mature (peripheral) B cell neoplasms:
Hodgkin lymphomas:
Notes:
  • New disease entities or subtypes of an entity are in italics
  • Asterisk (*) denotes provisional entities or subtypes
Prior classification systems
  • Rappaport classification:
    • 1956, revised 1966
    • Developed before lymphocytes were classified as B and T cells
    • Includes well differentiated lymphocytic lymphoma, poorly differentiated lymphocytic lymphoma and histiocytic lymphoma (Cancer Res 1966;26:1082)
  • Lukes-Collins classification:
    • 1974; classified non-Hodgkin lymphomas as B cell, T cell, histiocytic and unclassifiable types (Cancer 1974;34:1488)
  • Working formulation:
    • 1982; classified as low, intermediate or high grade; nodular versus diffuse; small, large or mixed tumor cell size (Cancer 1982;49:2112)
  • Kiel classification:
  • REAL (Revised European American Lymphoma):
    • Integrated clinical, morphologic, immunohistochemical and molecular characteristics
    • Included non-Hodgkin lymphoma, lymphocytic leukemias, plasma cell neoplasms
    • Excludes histiocytic neoplasms
    • Tumors not classified as low grade / high grade since one entity could have both types (Blood 1994;84:1361)
  • World Health Organization (WHO) 2008 classification:
    • Based on worldwide consensus on lymphoma diagnosis and was focused on the recognition of distinct diseases, using a multidisciplinary approach
    • Refined the definitions of well recognized diseases
    • Identified new entities and variants
    • Recognized provisional entities due to insufficient evidence to recognize them as distinct diseases at the time
    • Acknowledged the presence of borderline B cell lymphoma lesions, e.g. those with features intermediate between DLBCL and Burkitt and those with features intermediate between DLBCL and classic Hodgkin (Blood 2011;117:5019)
Board review style question #1
Which of the following is true regarding the 2016 WHO classification of B cell lymphoid neoplasms?

  1. Provisional lymphoma entities, such as large B cell lymphoma with IRF4 rearrangement, are those from the previous classification that are either transitioning to be merged with another entity or expected to be phased out
  2. Determination of cell of origin for diffuse large B cell lymphoma is required and can be performed by immunohistochemistry
  3. B lymphoblastic leukemia / lymphoma is considered to be a single entity in order to facilitate and simplify clinical trial enrollment of patients
  4. By definition, monoclonal B cell lymphocytosis has a lower limit of 5 × 10⁹/L cells in the blood
  5. High grade double hit B cell lymphoma characteristically includes TP53 and BCR-ABL gene rearrangements
Board review answer #1
B. Determination of cell of origin for diffuse large B cell lymphoma is required and can be performed by immunohistochemistry. This lymphoma entity is divided into germinal center B cell type and activated B cell type.

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Reference: WHO classification - B cell
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