Acute Myeloid Leukemia with a Masked Type of Three-Way t(8;11;21) Revealed by Fluorescence In Situ Hybridizations Using AML1-ETO Probe.

The translocation (8;21)(q22;q22) is associated with acute myeloblastic leukemia (AML) with M2 subtype. The accurate detection of this chromosomal rearrangement is vital due to its association with a favorable prognosis. Variants of t(8;21)(q22;q22) involving chromosomes 8, 21 and other chromosomes account for approximately 3% of all t(8;21)(q22;q22) in AML. Variants in some cases present as hidden translocations, and in such cases it is often difficult to confirm the presence of t(8;21)(q22;q22) by conventional cytogenetic analysis alone. The molecular detection of the AML1-ETO fusion gene is possible by reverse transcriptase polymerase chain reaction (RT-PCR) or dualcolor fluorescence in situ hybridization (FISH) using probes specific for AML1 and ETO. The mechanism described for variant formation is one step or two steps. We report a case of AML with a masked variant translocation. Conventional cytogenetics and FISH study was carried out on a bone marrow sample of the patient at diagnosis. Karyotype result at diagnosis revealed t(8;11)(q22;p15) by G-banding. FISH nalysis disclosed a 3-way translocation involving chromosomes 8, 11, and 21 and identified a masked variant t(8;21)(q22;q22) using AML1-ETO probe and whole chromosome paint probes (WCP) 8 and 11 with a one-step mechanism. FISH analysis with the AML1 and ETO probes is extremely valuable in cases of AML-M2 because of its ability to reveal masked t(8;21) (q22;q22) translocations and thus quickly confirm the diagnosis, allowing patients to be assigned to the correct risk group in terms of treatment. Simple variants of the t(8;21) translocation involving chromosome 8 and a chromosome other than number 21 are rare. Our case illustrates the challenge of recognizing complex aberrations that occur with variant t(8;21) and further reinforces the utility of FISH applications on metaphase for more accurate characterization of chromosome abnormalities which can lead to more precise therapeutic stratification.