A neoplasm of lymphoblasts committed to B-cell lineage. Most cases involve blood and bone marrow (B lymphoblastic leukaemia, B-ALL), a few present with primary nodal or extanodal tissue deposits (B lymphoblastic lymphoma, B-LBL).
Epidemiology
B-ALL is predominantly a disease of childhood (75% of cases <6 years old). B lymphoblastic lymphoma constitutes ~10% of cases of lymphoblastic lymphoma and 75% of cases are less than 18 years old.
Clinical features
B-ALL usually presents with bone marrow failure (thrombocytopenia/anaemia/neutropenia). The leukocyte count may be low, normal or raised. B-ALL also involves the CNS, lymph nodes, spleen, liver and gonads. B-LBL commonly involves skin (often as multiple nodules) , bone, soft tissues and lymph nodes.
Histopathology
Small to medium-sized blast cells with scantly cytoplasm. Nucleoli are inconspicuous.
Bone marrow: the blasts are relatively uniform with round/oval indented, sometimes convoluted, nuclei. Nucleoli are variable but usually inconspicuous. Mitotic figures are less common than in T-ALL.
Lymph nodes in B-LBL; there is usually diffuse involvement but sometimes paracortical infiltration. Cytology as for the bone marrow. Mitoses usually frequent. There may focally be "starry sky" pattern.
Immunohistochemistry 80%-90% of cases show an immature B cell immunophenotype:
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immunoreactivity |
notes |
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+ |
nuclear positivity is unique to LBL |
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most cases, except for
t(4;11)(q21;q23 ) ALL which is usually negative |
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may be positive |
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CD19† |
almost always |
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variable |
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variable |
cytoplasmic staining is considered lineage-specific |
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CD24 |
most cases, except for t(4;11)(q21;q23 ) ALL which is frequently negative |
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may be positive |
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variable |
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+ |
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Surface Ig |
rarely positive |
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myeloperoxidase |
- |
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cytoplasmic m heavy chain |
+ |
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†: fresh frozen tissue only
Differential diagnosis
Lymph nodes and extranodal tissue: in children, Burkitt lymphoma. In adults, blastoid variant of mantle cell lymphoma Positivity for TdT readily distinguishes LBL.
Myeloblastic infiltration is positive for chloroacetate esterase, myeloperoxidase and lysozyme.
References
World Health Organization Classification of Tumours, Tumours of the haematopoietic and lymphoid tissues, IARC Press 2001.
This page last revised 16.12.2002.
©SMUHT/PW Bishop