Cytogenetically cryptic AML1-ETO and CBF beta-MYH11 gene rearrangements: incidence in 412 cases of acute myeloid leukaemia

The rearrangements t(8;21)(q22:22) and inv(16)(p13q22) are two of the most frequently seen in acute myeloid leukaemia (AML), accounting for 8% and 4% of cases respectively. Detection of these abnormalities is important for di sease management as both are associated with good responses to conventional chemotherapy and prolonged disease-free survival, Recent reports using rev erse transcriptase polymerase chain reaction (RT-PCR) suggest that signific ant proportions of AML cases without a visible t(8;21) or inv(16) show expr ession of an abnormal fusion gene transcript and, consequently, they could not be detected using conventional cytogenetic analysis alone. We present h ere a four centre study involving 412 cases of AML screened using both stan dard cytogenetics and RT-PCR for AML1-ETO and CBF beta -MYH11, We detected a cytogenetic t(8;21) in 31 out of 412 (7.5%) cases and an inv(16) or t(16; 16) variant in 27 out of 412 (6.6%) cases. RT-PCR detected only two cases ( 0.5%) of cryptic t(8;21) and no instances of cryptic inv(16), Both cryptic t(8:21) cases had the classic M2 FAB morphology for this type of disease. O ur data concur with the established FAB type distribution of the rearrangem ents and indicate that cryptic t(8;21) and inv(16) may be much less frequen t than reported elsewhere.