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acute lymphoblastic leukemia

Sunday 30 May 2004

acute lymphoid leukemias, ALL: acute lymphoblastic leukemias

Images

- acute lymphoblastic leukemia T in bone marrow

Types

- B-cell acute lymphoblastic leukemia / B-cell ALL
- T-cell acute lymphoblastic leukemia / T-cell ALL

FAB and WHO classifications

The FAB classification system described three subtypes of ALL (L1, L2, and L3), defined by individual cytologic features such as cell size, nuclear chromatin pattern, nuclear shape, nucleoli, and amount of basophilia in the cytoplasm. The subtype L1 accounts for over 80% of the ALL cases in children and consists of predominantly small cells, up to twice the diameter of a small lymphocyte. The majority of adult cases of ALL are of subtype L2. These cells are larger than cells in L1 and are often heterogeneous in size. This distinction, however, is often arbitrary and provides little guidance for the management of individual patients. Consequently, it has been abandoned.

The WHO classification recognizes only precursor B cell acute leukemia (B-ALL) and precursor T cell acute leukemia (T-ALL).

Burkitt type ALL

The least common form of ALL, seen in approximately 3% to 4% of both children and adults, was termed L3, and is now called Burkitt type ALL. In this subtype, the cells are morphologically identical to the neoplastic cells in Burkitt lymphoma. The cells are large and uniform, with finely stippled chromatin and regular nuclear shape. Nucleoli are often prominent. Cytoplasm is moderately abundant and deeply basophilic. It is important to recognize this variant because initial treatment differs markedly from that of other ALL subtypes.

Cytochemistry

Cytochemical evaluations of blast cells in ALL reveal characteristic patterns. By definition, stains for lysosomal enzymes such as myeloperoxidase or the Sudan black reaction must be negative to support a diagnosis of ALL.

The periodic acid-Schiff reaction will reveal clumpy positivity caused by glycogen in ALL blasts (except Burkitt type, which reacts negatively) but is a poor discriminator of cell lineage because many AML cells will also react positively.

Chloroacetate esterase and lysozyme stains are negative in ALL, but α-naphthyl acetate esterase may be positive in T lymphoblasts.

ALL blast cells contain the enzyme terminal deoxynucleotidyl transferase (TdT), which, when present in the great majority of cells, is a fairly reliable marker for ALL.

Burkitt ALL cells often stain positively with oil red O because of the neutral lipid within the cytoplasmic vacuoles.

Cytogenetics

- 11p13 (LMO2)

  • t(7;11)(q35;p13) (/LMO2)
  • t(11;14)(p13;q11) (LMO2/)

- t(1;15)(q10;q10) (18036400)

- trisomies

  • trisomy 4

- deletions

  • 9p21 deletion
    • 9p21 maternal region preferentially deleted

- MYB duplication by dup(6)(q22-q23)

- numerical changes of chromosomes 4, 10, 17 and 21

- high hyperdiploidy

  • Children with acute lymphoblastic leukemia (ALL) and high hyperdiploidy (>50 chromosomes) are considered to have a relatively good prognosis. The specific extra chromosomes are not random. (17431878)

- Philadelphia chromosome-positive acute lymphoblastic leukemia

Molecular biology

- ETV6-RUNX1 fusion gene (TEL/AML1)
- BCR/ABL fusion
- MLL gene rearrangements

References

- Pui CH, Relling MV, Downing JR. Acute lymphoblastic leukemia. N Engl J Med. 2004 Apr 8;350(15):1535-48. PMID: 15071128

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