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Diagnosis:
Accelerated Phase of Chronic Myelogenous Leukemia (CML)
ISCN: 47,XY,+8,t(9;22)(q34;q11.2)
Cytogenetics: Approximately 92% of patients
with chronic phase CML have the 9;22 translocation; approximately 8% have
a complex translocation involving chromosomes 9, 22, and a third chromosome;
and less than 1% of patients have a cryptic rearrangement that can only
be detected by FISH or molecular techniques. Patients usually remain in
chronic phase for about 3 years. The chronic phase is followed by disease
progression; the first sign of disease progression is often the emergence
of secondary chromosomal aberrations. Some of the most common secondary
changes include an extra chromosome 8, an isochromosome of the long arm
of chromosome 17 [i(17)(q10)], and an extra derivative chromosome 22 (Philadelphia
chromosome). Some less common recurring secondary aberrations include
an extra chromosome 17, 19, or 21, loss of one chromosome 7, 17, or Y,
or a 3;21 translocation.
Molecular: The gene at 9q34 is called
ABL and the gene at 22q11.2 is called BCR. The translocation creates a
gene fusion on the derivative chromosome 22; the fusion protein has increased
tyrosine kinase activity when compared to the ABL protein.
Web Links: Atlas of Genetics and Cytogenetics
in Oncology and Haematology
Metaphase/
Karyotype/ Answer/
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