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Diagnosing Acute Lymphoblastic Leukemia

Findings

Acute lymphoblastic leukemia is divided into early B-cell population (about 80%), T-cell (about 10-15%), and B-cell with surface immunoglobulin (< 5 %).

Patients with Philadelphia chromosome-positive acute lymphoblastic leukemia, have a poorer prognosis, and represent more than 20% of adult cases.

About 95% of all types of acute lymphoblastic leukemia (except for B-cell) have elevated terminal deoxylnucleotidyl transferase (TdT) . If this marker is negative, the diagnosis of acute lymphoblastic leukemia is doubtful.

Acute B-lymphoblastic leukemia / B-lymphoblastic lymphoma, L1  or L2

  • Originates from precursor B-cells
  • Defined by lymphoblastic morphology L1 or L2
    • L1 – blasts with very little cytoplasm (< 15 of nucleus area), and less than 5% promyelocytes, negative diaminobenzidine peroxidase (DAB staining)
    • L2 – less than 5% promyelocytes, more cytoplasm than L1
  • Immunophenotype like immature B-cells

Acute T-lymphoblastic leukemia / T-lymphoblastic lymphoma, L1  or L2

  • Originates from precursor T-cells 
  • Defined by lymphoblastic morphology L1 or L2
    • L1 – blasts with very little cytoplasm (< 15 of nucleas area), and less than 5% promyelocytes, negative diaminobenzidine peroxidase (DAB staining).  
    • L2 – less than 5% promyelocytes, more cytoplasm than L1
  • Immunophenotype like immature T cells
  • CD1a is negative for Pro tT and mature T-ALL, positive for cortical T-ALL

Burkitt's leukemia/ lymphoma L3

  • Orginates from more "mature" B-cells 
  • Defined by lymphoblastic morphology (deep basophilic cytoplasm, vacuoles, FAB L3)
  • Immunophenotype like mature B-cells
  • Characteristic karyotype
  • These leukemia cells usually have three translocations: t(8;14), t(2;8), and t(8;22).

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