Fluorescence in situ hybridization analysis of masked (8;21)(q22;q22) translocations

The translocation (8;21)(q22;q22) is associated with acute myeloblastic leu kemia (AML M2). The accurate detection of this chromosomal rearrangement is vital due to its association with a favorable prognosis. Variant transloca tions exist; these may be hidden within an unusual or complex karyotype. Tn such cases, it is often difficult to confirm the presence of t(8;21)(q22;q 22) by conventional cytogenetic analysis alone. The molecular detection of the AML1/ETO fusion gene is possible by reverse transcriptase polymerase ch ain reaction (RT-PCR) or dual-color fluorescence in situ hybridization (FIS H) using probes specific for AML1 and ETO. Four cases of AML M2, with unusu al or complex structural chromosomal abnormalities, without cytogenetic evi dence of the classical t(8;21)(q22;q22), were studied by FISH. Two were AML 1/ETO positive bq RT-PCR, one showed a rearrangement by AML1 by Southern an alysis, and the fourth had morphological features characteristic of t(8;21) . The FISH results showed a co-localization of one AML1 and one ETO signal in interphase and metaphase nuclei in all four cases, demonstrating the pre sence of variant t(8;21)(q22;q22) rearrangements. There fore, FISH analysis with the AML1 and ETO probes is extremely valuable, in cases of AML M2, be cause of its ability to reveal masked t(8;21)(q22;q22) translocations and t hus quickly confirm the diagnosis, allowing patients to be assigned to the correct risk group in terms of treatment. (C) Elsevier Science Inc., 1999, All rights reserved.