Cytogenetic chromosomal analysis and DNA ploidy studies
are important diagnostic and prognostic factors in
More than half of all leukemias have detectable chromosomal abnormalities
by karyotypic analysis. Many chromosomal abnormalities are associated
with particular subtypes of leukemia, and appear to have prognostic
The Philadelphia Chromosome
Commonly Used Abbreviations
Oncogenes, genes for growth factors and genes for growth factor
receptors are often located in the region of the breakpoints.
In the example above, the c-abl oncogene at 9q34, coding for the
tyrosine protein kinase p145, is translocated to the bcr (breakpoint
cluster region) on 22q. This results in a new and abnormal fusion
gene, producing bcr/c-abl mRNA. This mRNA synthesizes a potent
tyrosine protein kinase p210 unique to chronic myelogenous leukemia.
The p210 protein may be instrumental in the genesis of CML.
The following is a partial list of chromosomal abnormalities
associated with particular subtypes of leukemia. Abnormalities
are detected in 50-60% of de novo acute myeloblastic leukemias
and more than 66% of acute lymphoblastic leukemias.
****2YMS should know t(8;21), t(15;17), t(8;14), t(9;22), and the
5q- chromosome abnormalities and the diseases associated with
each. See course objectives.
The frequency of chromosomal abnormalities in patients with a
previous myelodysplastic syndrome, history of radiotherapy or
history of chemotherapy approaches 100%
The prognosis of acute leukemia arising in these settings is poor.
The following chromosomal abnormalities are poor prognostic indicators:
*associated with myelodysplastic syndromes
Other poor prognostic factor are advanced age at the time of
diagnosis, and severe leukocytosis.
Different chromosomal abnormalities are associated with different
characteristic features. For example, Auer rods are often associated
with t(8;21) and t(15;17). Eosinophils have been associated with
abnormalities of 16q22, and this is a good prognostic indicator.
inv(16), t(8,21) - respond better to high dose cytarabine.
del(5q), del(7q) trisomy 8, and abnormal IIq - poor response
Certain translocations are closely associated with ALL:
B-cell lymphoid malignancies:
The following translocations place the c-myc
oncogene next to different immunoglobulin genes
- t(8;14) (q24;q32) - IgH on 14
- t(8;22) (q24;q11) - IgL on 22
- t(2;8) (p12; q24) - IgK on 2
FYI: T-cell lymphoid malignancy - t(10;14) (q24;
q11): a protooncogene on chromosome 10 is translocated to a
region of TCR alpha-chain (14q11).
Practice Question #1
A 31-year-old white male coal miner, comes to you because of a persistent
cold that began 3 wks ago. There is no lymphadenopathy or hepatomegaly.
His WBC was 12.0 x10 /L with 45% blasts. A marrow aspirate &
biopsy showed 80% blasts. The morphologic and cytochemical studies
are equivocal, (ie. nondescript blasts with negative MPO, PAS,
and NSE. Immunologic studies) were unavailable.
What is the most likely diagnosis based on the
A. Acute myeloid leukemia, M2
B. Acute myeloid leukemia, M3
C. Acute lymphoblastic leukemia, L1
D. Acute lymphoblastic leukemia, L3
E. Chronic myelocytic leukemia
Leukemia: Laboratory Evaluation - DNA
The number of chromosomes or ploidy of leukemic cells is
especially important in childhood ALL, where the
hyperdiploid ALLs have a better prognosis than diploid or
Approximately 25-30% of childhood ALLs are hyperdiploid (>50
chromosomes); 15% are hyperdiploid (47-50 chromosomes); 5-10%
are hypodiploid (<46 chromosomes); <1% are tetraploid or
near tetraploid; and the remainder diploid.
Ploidy is determined by karyotype or by measurement of cellular
DNA content. The following discussion will teach you how to determine
ploidy by measuring cellular DNA content.
Cells are stained with a fluorescent dye (propidium iodide) that
binds to DNA. The fluorescence is measured by flow cytometry.
The degree of fluorescence reflects the amount of cellular DNA.
A DNA index of >1.15 corresponds to >52 chromosomes or hyperdiploidy.
A DNA index of 1.0-1.15 is diploid or hyperdiploid 47-50. A DNA
index of <1.0 corresponds with hypodiploidy.
The Cell CycleNormal
In A, the DNA index of a leukemic bone marrow (60% blasts;
40% normal myeloid & erythroid) is abnormally high (>1.15)
indicating hyperdiploidy. Note the normal G0/G1 peak from the
normal marrow cells present.
In B, marrow cells (>90% blasts) with features
of ALL-L3 Burkitt's are hypodiploid (DNA index
<1.0).There is a high proliferative fraction, as measured
by the cells in S phase. This is characteristic of high
****2YMS should know ALL-L3 are hypodiploid with a high
proliferative fraction characteristic of high grade
leukemia/lymphoma. See course objectives.
Practice Question #2
A 5-year-old boy is noted by his mother to have tiny "pin-point"
bruises on his legs and arms. You ask his mother to bring him
to the office today. He appears pale and frightened. No hepatosplenomegaly,
nor lymph-nodes are noted. His WBC is 74.0 x10 /L with 86% blasts.
A marrow aspirate shows >90% blasts. Morphologic and cytochemical
(negative MPO & NSE; granular PAS positivity) studies are
consistent with lymphoblasts. Immunologic studies are c/w a pro-B
What is the prognosis based on the bone marrow DNA
A. average <8 week survival
B. average <12 month survival
C. average 24-36 month survival
D. average 60 month survival
E. average 10 year survival
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