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WHO Classification of Tumours
B lymphoblastic leukaemia/lymphoma, NOS
Tumours of haematopoietic and lymphoid tissues


Definition

B lymphoblastic leukaemia/lymphoblastic lymphoma is a neoplasm of precursor cells (lympho­blasts) committed to the B-cell lineage, typically composed of small to medium-sized blast cells with scant cytoplasm, moderately condensed to dispersed chromatin and inconspicuous nucleoli, involving bone marrow (BM) and blood (B acute lymphoblastic leukaemia/ALL) and occasionally presenting with primary involvement of nodal or extranodal sites (B lymphoblastic lymphoma/LBL). By convention, the term lymphoma is used when the process is confined to a mass lesion with no or minimal evidence of peripheral blood (PB) and BM involvement. With extensive BM and PB involvement, lympho­blastic leukaemia is the appropriate term. If the patient presents with a mass lesion and lymphoblasts in the BM, the distinction between leukaemia and lymphoma is arbitrary
Click to access Pubmed
Murphy SB (1978)
Childhood non-Hodgkin's lymphoma.
N Engl J Med 299: 1446-8



. For many treatment protocols, a figure of 25% BM blasts is used as the threshold for defining leukaemia.

In contrast to myeloid leukaemias, there is no agreed-upon lower limit for the percentage of blasts required to establish a diagnosis of lymphoblastic leukaemias. In general, the diagnosis should be avoided when there are fewer than 20% blasts. Presentations with low blast counts can occur but are uncommon; currently there is no compelling evidence that failure to treat a patient when there are fewer than 20% BM lymphoblasts has an adverse effect on outcome.

> Exclusionary criteria
The term B-ALL should not be used to indicate Burkitt leukaemia/lymphoma . Furthermore, some cases of B-ALL/LBL have specific recurrent genetic abnormalities that are associated with distinctive clinical and phenotypic properties, have important prognostic implications or demonstrate other evidence that they are mutually exclusive of other entities. These cases should not be classified as B lymphoblastic leukaemia/lymphoma, NOS, but are classified according to their genetic abnormalities. Currently there are seven genetically defined B lymphoblastic leukaemias/lymphomas:
B lymphoblastic leukaemia/lymphoma with t(9;22)(q34;q11.2);BCR-ABL1 ,
B lymphoblastic leukaemia/lymphoma with t(v;11q23);MLL rearranged ,
B lymphoblastic leukaemia/lymphoma with t(12;21)(p13;q22); TEL-AML1 (ETV6-RUNX1)
B lymphoblastic leukaemia/lymphoma with hyperdiploidy ,
B lymphoblastic leukaemia/lymphoma with hypodiploidy (hypodiploid ALL) ,
B lymphoblastic leukaemia/lymphoma with t(5;14)(q31;q32);IL3-IGH ,
B lymphoblastic leukaemia/lymphoma with t(1;19)(q23;p13.3) E2A-PBX1(TCF3-PBX1) .

> Related Topics
Introduction: Classification of lymphoid neoplasms