What is the role of immunophenotyping in the workup of pediatric acute lymphoblastic leukemia (ALL)?

Updated: Jan 03, 2019
  • Author: Vikramjit S Kanwar, MBBS, MBA, MRCP(UK), FAAP; Chief Editor: Jennifer Reikes Willert, MD  more...
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Answer

Acute lymphoblastic leukemia (ALL) cells rearrange their immunoglobulin and T-cell receptor (TCR) genes and express antigen receptor molecules that correspond to such processes in normal developing B and T lymphocytes, so that ALL can be classified as B-lineage or T-lineage ALL.

Mature B-cell ALL should be differentiated from other B-lineage ALL and accounts for only 1-3% of childhood ALL. Diagnosis depends on the detection of surface immunoglobulin on leukemic blasts, as well as distinctive morphology, with deeply basophilic cytoplasm containing prominent vacuoles, designated L3 in the French-American-British (FAB) system (see Histologic Features).

B-lineage ALL accounts for 80% of childhood ALL and involves lymphoblasts that have cell-surface expression of 2 or more B-lineage–associated antigens (ie, CD19, CD20, CD24, CD22, CD21, or CD79). [4] CD10 is commonly expressed, which makes it a useful diagnostic marker, and the presence of aberrant myeloid markers (eg, CD7) is occasionally noted but has little prognostic impact. B-cell precursors of ALL can be further subclassified as early pre–B-cell, pre–B-cell, or transitional pre–B-cell, but distinguishing these subtypes is usually not clinically relevant.

T-lineage ALL accounts for 10-15% of childhood ALL, and is identified by the expression of T-cell–associated surface antigens, of which cytoplasmic CD3 is specific. T-cell ALL cases can be classified by early, mid, or late thymocytes, and 10% of cases are early T-precursor (ETP) ALL characterized by absent CD1a and CD8, weak CD5, and one or more myeloid or stem cell markers (eg, CD117, CD34, CD13, CD33). ETP ALL is thought to have worse prognosis, but this assumption may not be valid on modern T-cell ALL chemotherapy protocols.

The overall outcome for T-lineage and high risk B-lineage ALL is similar, provided intensive chemotherapy is used.


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