Low incidence of TEL/AML1 fusion and TEL deletion in Korean childhood acute leukemia by extra-signal fluorescence in situ hybridization

TEAL/AML1 fusion in acute leukemia results from cryptic translocation of ch romosome 12 and 21, the presence of which suggests a favorable prognosis. T he incidence of TEL/AML1 fusion in B-lineage ALL is approximately 25%, but the incidence in Korea has not yet been reported. To investigate the incide nce of TEL/AML1 fusion and TEL deletion, bone marrow specimens from 77 Kore an children with newly diagnosed acute leukemia were analyzed by FISH. We a pplied extra-signal FISH to discriminate a true TEL/AML1 fusion from a fals e-positive fusion signal. To determine the cut-off value of the TEL/AML1 fu sion signal, 20 normal bone marrow specimens and 28 normal peripheral blood specimens were also analyzed. The frequency of patients with TEL/AML1 fusi on was 13.3% (4 cases) among 30 B-lineage ALL and 9.5% among 42 ALL. One TE L/AML1 fusion-positive patient was also found among 4 acute biphenotypic le ukemias. TEL/AML1 fusion was not found in any samples from patients with T- lineage ALL or AML. The incidence of TEL deletion was 6.7% (2 cases) among 30 B-lineage ALL and 4.8% among 42 ALL. The incidences of TEL/AML1 fusion a nd TEL deletion in Korean children with acute leukemia appear to be lower t han those in other countries, suggesting a racial difference. (C) 2001 Else vier Science Inc., All rights reserved.