A c u t e L y m p h o b l a s t i c L e u k e m i a
Definition
• Acute lymphoblastic leukemia (ALL) is a malignant proliferation of
lymphoblasts in the bone marrow and blood.
• There is no 20% cutoff for diagnosis like there is in AML. Most of the time, at
least at initial diagnosis, there is an overwhelming number of lymphoblasts
present in both blood and marrow.
• ALL is the most common type of leukemia in children (80-85% of childhood
leukemias).
• ALL also occurs in adults, however.
Classification
The classification of ALL is based on the immunophenotype of the lymphoblasts. (This is different from the classification of AML, which is based on morphology, genetics, and to a lesser extent immunophenotype and cytochemical staining pattern).
TdT T-cell Ag B-cell Ag CIg SIg
T-cell ALL + + - - -
Early B-cell precursor ALL + - + - -
Pre-B-cell ALL + - + + -
B-cell ALL - - + - +
ALL: Subtypes
T-cell ALL
• 15% of cases of ALL.
• Blasts positive for TdT and T-cell markers (e.g., CD2, CD5).
• May see T-cell receptor rearrangement (using molecular studies).
• Prototypic patient: Teenage male with mediastinal (thymic) mass, very high
WBC.
• Bad prognosis.
B-cell precursor ALL
• Early B-cell precursor ALL
• "Common" subtype
• >50% of all cases of ALL.
• CD10 ("CALLA") +.
• t(9;22) (Philadelphia chromosome) in minority of patients.
• Best prognosis of all types - except cases with t(9;22) (poor prognosis).
• 10% of all cases of ALL.
• CD10 ("CALLA") -.
• Intermediate prognosis.
• Pre-B-cell ALL
• 20% of all cases of ALL.
• Blasts express monoclonal cytoplasmic Ig.
• Intermediate prognosis.
B-cell ALL
• 1-3% of all cases of ALL.
• Characteristic morphology (big cells with deep blue cytoplasm and vacuoles).
• Blasts express monoclonal Ig on cell surface, and are TdT negative.
• t(8:14).
• Identical to Burkitt’s (small non-cleaved cell) lymphoma morphologically,
immunophenotypically, and clinically.
• Prototypic patient: older child/young adult with abdominal mass.
• Extremely fast-growing (but because of this, also very sensitive to
chemotherapy!)
Treatment and Prognosis
• Prognostic factors
• Immunophenotype (Best: "common" early B-cell precursor)
• Age (Best: 1-10y.)
• WBC (Best: <10,000)
• Cytogenetics (Best: hyperdiploidy)
• Treatment
• Chemotherapy with or without bone marrow transplant.
• Many children now appear to be cured with current therapy.
