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2 Acute Lymphoblastic Leukemia

13

 

 

2.4.4.1Terminal Deoxynucleotidyl Transferase

Deoxyribonuclease (DNase)

Activity in all circulating ALL cells, with the exception of mature B-cell ALL

Terminal deoxynucleotidyl transferase (TdT) is absent in normal lymphocytes

2.4.4.25-Nucleotidase

Decreased level of 5-nucleotidase in T lymphoblasts

Overview of biochemical and clinical characteristics

 

Pre-B-cell ALL

T-Cell ALL

B-cell ALL

TdT

+

+++

+

5-Nucleotidase

++

 

++

Glucocorticoid receptor

++

+

+

Initial white blood cell count

Low

High

Low or high

Extramedullary leukemia

+

+++

 

Ratio of males to females

Equal

4:1

 

Peak age (years)

4

9–12

Not known

Organomegaly

++

++++

 

Percentage of cases

80

15

1–3

2.4.5Cytogenetic Characterization

In 85% of children with leukemia, an abnormal karyotype in the malignant clone is detectable

The analysis combines chromosome banding with fluorescence in situ hybridization (FISH) with spectral karyotyping (SKY) and with comparative genomic hybridization (CGH)

The cytogenetic abnormalities reflect the number of chromosomes (ploidy) and the structure of chromosomes (rearrangements)

The DNA index (DI) defines the cellular DNA content, determined by flow cytometry

 

 

DI

 

 

Normoor pseudodiploid cells

1.0

Normal DNA content

Hyperdiploid

 

>1.0

>1.1: 53 chromosomes/cell

Hypodiploid

 

<1.0

 

 

Percentage of DNA index in ALL

 

 

 

 

Number of

Rate (percentage)

Prognosis

 

chromosomes

 

 

Hypodiploid

41–45

 

6 < 3

Unfavorable

Pseudodiploid

46

 

41.5

Various

Hyperdiploid

47–50

 

15.5

Favorable

 

>50

 

27.0

 

Normal diploid

46

 

8.0

 

14

 

P. Imbach

 

 

Structural chromosomal abnormalities

 

Immunophenotype and

Oncogene/hybrid

Rate Prognosis

translocation

fusion gene

 

t(12;21)

TEL-AML-1

25% good prognosis

Precursor-B/T-cell ALL

 

 

t(9;22)

BCR-ABL

3–5%, unfavorable prognosis

Philadelphia chromosome

 

 

Precursor-B ALL

 

 

t(1;19)

TCF3 (alias

25% moderate prognosis,

 

E2A-BX I)-PBX1

often high WBC

t(4;19;11)(11q23)

AF4-MLL

Predominantly infants with poor

 

 

prognosis, 3% in other ALL

t(12;21)

ETV6 (alias

Good prognosis

 

TEL)-RUNX1

 

 

(previously AMLI)

 

T ALL

 

 

t(11;14)

LMO1 (alias TTG1)/

Predominantly males,

 

LMO2 (alias

extramedullary ALL

 

TTG2 – TCRD fusion)

 

B ALL

 

 

t(8;14)

MYC – IGH fusion

Predominantly males, L3 morphology,

t(8;22)

 

with intensive chemotherapy, moderate to

t(2;8)

 

good prognosis

 

 

Some examples of cytogenetic alterations are:

Translocation t(9;22) (BCR-ABL fusion protein) is present in 3–5% of children with ALL (and in most children with CML) and is characterised by a protein with tyrosine kinase activity, with the ability to immortalize progenitors. Tyrosine kinase inhibitors such as imatinib turn the prognosis favorably

The structural abnormality of chromosomal band 11q23 is detected in 5–10% of childhood leukemias, 60–70% of leukemias in infants (ALL and AML), and in 85% of secondary leukemias. The 11q23 abnormality [also called mixed-lineage leukemia (MLL) protein] is an important regulator of pluripotent cells. Fusion partners with MLL are also observed on chromosomes 4, 6, 9, and 19 of precursor ALL [i.e., t(4;11)(q21;q23)]. 11q23/MLL/AF4 abnormalities are correlated with a poor prognosis

Chromosomal abnormalities disappear during remission (see Minimal Residual Disease, Chap. 1) and often reappear during relapse of ALL

2.4.6Cytometry

Flow cytometry can measure the DNA and RNA content of individual cells. It provides:

The incidence of cells in different phases of the cell cycle

The determination of the DNA content of leukemic cells for prognostication (ploidy)

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