[Study of the childhood acute lymphoblastic leukemia with t(12;21)].

OBJECTIVE

To explore the incidence, clinical characteristics and prognosis of childhood acute lymphoblastic leukemia (ALL) with t(12;21).

METHODS

t(12;21)/TEL-AML1 fusion gene was examined in bone marrow or peripheral blood mononuclear cells from 51 newly diagnosed childhood ALL patients by conventional cytogenetic R-banding analysis (CCA), dual colour interphase fluorescence in situ hybridization (I-FISH), and nested reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

t(12; 21)/TEL-AML1 fusion gene was found in 11 cases by FISH or PCR, accounting for 21.6% and 26.9% in childhood ALLs and in non-T lineage ALL cases, respectively. The median age at diagnosis was 6.8 (2.9 to 12) years. All of the t(12;21) patients expressed non-T lineage immunophenotype, and most of them were common-ALL. High myeloid antigen coexpression was not found. In 11 CCA cases, normal karyotype was found in 7, and a dubious t(12;21) in one. TEL allele deletion was found in 8 (72.7%) of t(12;21) positive cases by FISH. By comparison, no statistic difference was found in sex, anemia, hemorrhage, organ enlargement, and initial WBC count between the positive and negative non-T lineage ALLs, but the platelet count and the frequency of IgH gene rearrangement were much lower in positive cases (P = 0.008 and 0.007, respectively). Moreover, no difference was found in overall CR rate, CR rate within 4 weeks, CR duration and relapse rate between the two groups.

CONCLUSION

t(12;21) was the most common chromosomal translocation in childhood ALL, but not all of them could be detected by CCA. t(12;21) cases showed non-T cell immunotypes, most of them were CD(10)(+) ALL. TEL allele deletion was common in these cases. There was no significant difference in clinical characteristics and short term outcome between the t(12;21) and the TEL-AML1 negative cases. In our data, Chinese t(12;21) ALL showed older in age, lower BPC, lower IgH rearrangement frequency and more of normal karyotype as compared with the reports abroad.