Chronic myeloid leukemia with a rare variant Philadelphia translocation: t(9;22;21)(q34;q11;q22)

A chronic myeloid leukemia case with a unique variant Philadelphia translocation: t(9;22;21)(q34;q11;p12)

The so-called Philadelphia (Ph) chromosome is present in more than 90% of chronic myeloid leukemia (CML) patients. Approximately, 5-10% of these patients show complex translocations involving a third chromosome in addition to chromosomes 9 and 22. Since at present the majority of CML cases are treated with imatinib, variant rearrangements do not exhibit specific prognostic significance. However, events of therapy resistance remain to be studied. In this study, we report a unique case of CML exhibiting an uncommon t(21;22)(p12;q11). This translocation has been characterized by fluorescence in situ hybridization (FISH) and array-proven multicolor banding (aMCB). Using specific probes for the BCR and ABL genes, results of FISH showed a three-way variant Philadelphia translocation (9;22;21)(q34;q11;p12) with a BCR/ABL fusion residing on the der(22) and the 3'BCR region translocated on the short arm of the derivative chromosome 21. In addition, the aMCB technique is significant in the detection of the breakpoints of genetic changes. The underlying mechanisms and prognostic significance of these changes are discussed.

Contribution of fluorescence in situ hybridization analyses to the characterization of masked and complex Philadelphia chromosome translocations in chronic myelocytic leukemia

Bone marrow samples from 112 patients with chronic myelocytic leukemia were investigated using cytogenetic methods. Fluorescent in situ hybridization (FISH) with whole-chromosome paints and BCR-ABL probes was used to confirm and/or complete the banding findings when a variant or a masked Philadelphia chromosome (Ph) translocation was found. Eight variant Ph translocations were identified. Three-way Ph translocations were found in seven patients. Chromosome 4 was involved in two of these cases and chromosomes 3, 11, 14, 17, and 16 in one case each; in the patient with chromosome 16 involvement, a ring of the translocated chromosome 9 was identified, that is r(9)t(9;16;22). The eighth patient had a five-way Ph translocation: t(2;9;16;22;22). The BCR-ABL fusion gene was detected on the Ph chromosome in all eight cases; two cases presented also a deletion of the 5' ABL region on the derivative chromosome 9. In the five-way translocation, the 3' DNA sequence of the ABL oncogene was fused with the 5' DNA sequence of the BCR gene on the Ph chromosome and the 5' end of ABL was inserted into the other chromosome 22. A masked Ph chromosome was identified in one of the 112 patients; it involved the insertion of the 3' ABL into BCR on an apparently normal chromosome 22, resulting in the BCR-ABL fusion gene. In conclusion, FISH analyses allowed not only a more accurate characterization of complex Ph translocations with subtle abnormalities and the identification of cryptic rearrangements, but also the recognition of deletion of the 5' ABL region, which could carry with it a poor prognosis.

Chronic myeloid leukemia with a rare variant Philadelphia translocation: t(9;10;22)(q34;q22;q11)

We report a 59-year-old, male, chronic myeloid leukemia patient with a rare variant Philadelphia (Ph) translocation t(9;10;22)(q34;q22;q11). Fluorescence in situ hybridization with whole chromosome paints was used to confirm the cytogenetic findings. With a BCR/ABL-specific probe, the known rearrangement on the derivative chromosome 22 was found. The prognostic implications as well as the relevance of the additional breakpoint region 10q22 are discussed.